Here's a video by Maximilian Dood both reacting to Terry, while also having an interesting discussion of future DLC. The most interesting points he brings up are:
1. Early in the Switch's lifespan many old SNK games were released on the eShop and sold like hotcakes, which may have been where interest and talks about Terry coming to smash began
2. There is no truly impossible character that Sakurai could bring in at this point
3. The Tokyo Game Show is coming up in December, about a month before the theoretical window that character 5 would fall into (his guess is Monster Hunter due to the development of an exclusive game for the switch)
Conclusion: point #1 proves that exposure of even older titles matters. #2 is something we've already discussed here. I haven't really seen #3 talked about though, a reveal at TGS (most likely through a direct) seems somewhat reasonable