Sorry for coming late to this - I have wondered why the “reply as linked topic went missing”. We love that feature on our site, so would be happy if it returned to its visible place
perhaps the first option but instead of “plus new topic” , with 
or something instead of “plus” to indicate that you are replying, but creating a new thread.
This thread has already suggested ways for the feature to remain visible. “Open” posts can be reply-as-new-topicked by ticking a checkbox in the composer. “closed” ones can have the Reply button replaced with a Reply As New Topic button.
This feels way to rare a feature to be visible every time I look at the composer. Maybe behind the “gear”
The more I think about this and try to do linked topics with these new ideas in mind, the more I think this approach would be not circuitous but pure awesomeness. Sensible, easily discovered, and easily explained in case anyone is looking for it and asks.
+ New Topic and you’re off to the races, quoted text in place and ready to be used in a new post. 
I like the idea – the only difficult issue I can see is that the post link would have to not be auto selected anymore. Otherwise, your quote selection is un-selected.
How about right as we select the text?
Ok, so let’s try this 
https://github.com/discourse/discourse/commit/9588583244788c3c3a8695f016cc23b88df8dac4
It’s obnoxious, IMO, to show it every time you select text. It’s an uncommon action, and we don’t want to show the ejector seat button to the average user who is doing their commute to and from work…
Shouldn’t it be quoting the post you choose Reply as New Topic from? Or at least putting a link in the composer window? (keyboard shortcut shows the data it pulls in still)
As, right now, it doesn’t really serve a purpose without that context being put in automatically.
What about something like a split button off to the right of that, that just had a + glyph, or some indication that you could quote reply in a new topic? It would be less invasive, but keep the suggested functionality.
Hitting “quote reply” would keep the quote. Hitting on the “+” would reply in new topic.
Yes, as already proposed earlier in the topic? Perhaps exactly like that? 
Still not a fan.
Yes, this happens with a fair bit of frequency already on live Discourse sites. You really don’t want brand new users creating new topics, to be honest – they often don’t know what they’re doing.
The effect is less dramatic than on a Q&A site, but this advice still mostly applies: a site with a bunch of horrible topics on the homepage is not going to do well.
To put it another way, when I go to [Discourse] home page, I see a ton of [topic]s. If most of those are terrible [topics] with little to no indication that I’d be wasting my time by reading them, the value proposition of visiting and participating in [Discourse] is diminished: I have better things to do.
Compare that to [replies] on a specific [topic]: I’ve made a conscious choice to look into what I think is an interesting [topic]. I already made the decision that the [topic] is worth my time. If I find the [replies] to be useless, I have a few different options, as an interested party, to register my displeasure, including writing my own [reply].
Being able to write your own [reply] is key: if your [reply] is good enough, it’ll rise above the junk [replies] and everyone will be better off for it.
There is no such action for [topic] lists. I can’t say “these [topics] suck, show me this [topic] I just thought up instead”: that’d be silly.
It’s way less risky for experienced users to create topics. New users aren’t in a good position to create interesting, useful topics quite yet so you don’t want that action front and center for them.
Totally my fault. Just pushed a fix 
https://github.com/discourse/discourse/commit/7efd9359ec0995ac0d87e334e9705d838ea2f746
Whoops, I seem to have blanked on everything discussed previously, my bad.
Also, after playing around with it, I’m coming around to agreeing with the “why do you need to quote reply in new topic anyway?” side of the argument: Once you have a compose window open, it is really not difficult to select and quote after that. It would also have the same flow as copying multiple quotes into a new topic.
One more thing, prior they were referred to as a “Linked Topic”, now it is referred to as “New Topic”, does the clarification matter? 
Sorry, that is my own use of incorrect terminology, it actually should only embed “Continuing discussion from link to topic”, not quoting it.
Two separate issues:
The “continuing discussion…” vs blank I agree – should populate the new post with “continuing discussion…” in the composer.
The second issue that I was responding to above is the ability (or lack there of post-timeline) to select a hunk of text and hit “reply as new topic” and have the composer auto-populate with the quote. This was possible pre-timeline, but is no longer with the removal of the “reply as new topic” gutter link.
Oh, I see. Sorry. Yeah, and the placement of the “+ New Topic” prevents that from working, as your selection is removed when you click the post timestamp or the share button.
I think it’s fine to quote after the fact. Again, we’re talking about an extremely rare action in the system here. I’m not sure we need to gold plate this one…
Whilst not 100% on this idea, it might be reasonable include a menu option.
Perhaps the options here aren’t quite correct - but hopefully this shows the idea.
You could also perhaps slip “Official Warning” and “Whisper” in there as options too.
This would also open up a place to indicate a “call” type as required by Start a new conversation with a customer not yet in Discourse feature request.
The idea is to change the type of reply whilst editing.
In the same way as now clicking the reply button on a topic / post would continue to change the type / or update the “linked topic”.
Oh, that’s a really nifty idea. 
A bit of a power user hidden thing, but we could make that more obviously a button / selector as well.