Main battle tanks (MBT) have practically reached a dead-end in their development.
The Russian T-90 (a development of the T-72) has had some incremental upgrades since it’s introduction 30 years ago. It is Russia’s MBT.
It’s supposed successor, the brand new design T-14 has been in development hell and general production limbo since 2016. Though reasonable production and deployment has started.
the US Abrams has been incrementally production upgraded since its introduction in … 1980. There doesn’t seem to be a brand new replacement on the horizon.
the uk challenger II is from 1998 and some will be upgraded in near future to III specification, the rest used as spares/scrapped.
there’s also the German Leopard 2, the French leclerc , and iirc quite a few other homegrown ones - Japan, India, Brazil …
I think the tank , or at least the MBT, is at the end of its life.
I’m surprised there isn’t a MBT drone from anyone in the works… or a medium tank drone at least. But perhaps there is at some skunkworks.