Solo tower defence is definetly an interesting idea, it must be one of the most asked for things on the forums. I myself made a small suggestion here about it:
https://www.cubecraft.net/threads/solo-tower-defence.282749/ , the main concern about my suggestion was that its very like hypixels tower defence and cubecraft needs original content too
I and my friends then came up with the idea of a different type of 1v1 tower defence rather than a 1v1v1v1v1v1, basically a 1v1 but being able to send 12troops + 1troop per game minute(with a cap of 36) . that means that at minute 10 lets say it would be 12+10 = 22 troops, it would be very boring at late game only being able to send 12 troops, so with this basically we took 1 player as 3 so everything is x3 to make it less slow and boring as a normal 1v1. one day we will make a detailed suggestion
as for your asking if td will get an update, the "update" your talking about was just a balancing "update" i think they've pretty much confirmed that at some point there'll be a content update for tower defence but Cubecrafts priorities change a lot so idek anymore, maybe..... we can only hope