I have no idea when or if they'll do another batch, but at the very least a bunch more being in the world should hopefully make them less scarce and expensive on eBay, etc.
I missed both kickstarters, but their "shop" still had both models until early January 2021. I ordered one in October, but won't get it until August. I do enjoy these old retro computers and some games.
I find most of the original games to be unbearable (I didn't play games during that era so there isn't even nostalgia for me), but the new games people are building for the Spectrum and Commodore 64 are fun and a bit more modern in some respects. Ex: I recently bought Attack of the Petscii Robots and the graphics/music/gameplay/manual... everything is great. They're also more amenable to the very limited time I have in adulthood. I doubt I'll play another MMO until I retire.