True,

I have already asked cygnal about his.

They said later this year will come parts with more [1K and 2K] SRAM.

For the support of external memory, I don't have an answer yet
from them. I suppose they will not do it, due to timing related issues.

Perhaps try to emulate /RD /WR in software, for external RAM access.

As for now, I don't see other true alternatives.

Can you use an external serial memory device in your
application?