Hi, thank you for this nice insight, you look familiar with event organization.
I don’t think it is necessary except if anyone here has a relevant case use to propose: for me a 30 person event has a waiting list of 30 persons as well and it stops there as setting up a limit implies anticipating the number of people who are going to ‘unattend’ your event : if 30 people don’t participate because of bad weather at the last minute, it would make sens to have 30 spots free for bravest people 
on the waiting list.
You made me think that closing the waiting list implies 2 main situations and thus 2 similar features :
-One way being fully closing it making participants on the waiting list not able to get a free spot at all : If the event requires custom preparation for/from the participants you don’t want a spot to get attributed at the very last moment to someone on the waiting list who would come without its white tuxedo to the party
-Another way being partially closing it implying the unability to join the waiting list anymore while keeping the ability for people on it to still get a spot if one becomes avalable.
If we are talking about the case where the waiting list gets fully closed : once the event has started it is too late as you may want to let people know in advance that there is no possibility at all that they will be joining the event while thanking them for their interest as you suggested.
But it may be that it is what you suggest at the end of your message where you mention travelling time requirements?
Last point : I don’t want to hijack my feature request with another feature request but if this whole things gets setup I think it is important to let you know that people may ask in the future also for the ability for participants to join the event with external participants.
Example : on meetup.com you can create a 30 max participants event with the ability for each participant to mention that they will come with for example max 4 external participants : if a participant chooses to to come with 4 friends when the event still has 30 spots, then the remaining amount of spots available is now 25.
Sorry for the obvious maths, I just wanted to clarify this feature that might go along with the waiting list feature.