> Cell [...] can be developed futher. [...] single Cell can be developed and scaled further.

By whom?

> We could one day develop real innovative machine using main CPU all those
> programmable units.

Who is "we"?

> one unit could do MUI

I believe GUI classes are too intertwined with the actual program logic to allow for execution by something like Cell SPEs.

> Needed drivers can be ported from Yellow Dog Linux.

The use of the SPEs from OtherOS is openly documented.

> some new board can be developed around it

Of course that would be possible, but who should do it and why?

> YDL is yet not well optimized

And it won't be optimized for Cell any better as Fixstars gave up on the Cell years ago. The last YDL version supporting Cell was 6.2 in 2009. Starting with 6.2.1 in 2010, YDL went x86+CUDA, so no PPC support at all. With 7.0 in 2012, YDL has switched back to PPC, but this time POWER7-only, no Cell nor any other PPC.

> Maybe its even possible to do Cell PCI or PCI-E card

There're already Cell PCIe cards. As for Cell PCI cards, who should make them?