The latest research in fingerprinting works cross-browser, so that solves the “3 or 4 different web browsers” issue. With 8 different devices, that means you get 8 shots at being an annoying troll before you have to go out and drop real money on another device to continue your shenanigans. On the other hand, if you’re capable of keeping your inanity in check for a few initially moderated posts, you can then proceed to go hog-wild as many times as you like, because new accounts are essentially free.
Now, if you want to take my pie-in-the-sky device fingerprinting and turn it up to 11 (pie-in-the-asteroid-belt, perhaps?), how about a comprehensive “risk score” for each user, that takes into account the user’s innate characteristics (e-mail address, IP address, ASN, “using a tor exit node”, browser/device fingerprint, etc) as well as their behaviour (made an unflagged / approved post, got a like, gave a like, etc). The TL system is then augmented to require a risk score below a certain point in order to progress through the trust levels, in addition to all the other factors required for TL advancement.
The benefit of this is that you can put, say, TL0 on permapprove, and while “low risk” new users can progress in the usual fashion and not bother the mods too much, anyone “high risk” gets some additional attention, but without requiring mods to do too much manual leg work to keep track of potential shenaniganisers (trust me, that’s totally a word). Of course, someone who ticks all the “naughty” boxes and gets a super-high risk score can get autobanned or be manually approved before doing anything, or whatever seems appropriate.
And you thought just implementing fingerprinting would be a big job.