But it seems like the SGI Challenge architecture makes more sense in 1995. An Onyx would be half the price of that Y-MP, with superior graphics. A Power Challenge GR would as performant as the Y-MP, again with superior graphics, though I suspect about the same price. And anything from SGI has better OS and development tools than UNICOS did at the time. Plus they're easier to install, power and cool.
I suspect that moving over to Win32 probably conferred a lot of advantages, developing on the same system that is your target market. I wonder if they would have ultimately done that even if the Cray deal was on the table.
As someone who used both: it also would be a massive downgrade in terms of reliability and system stability. The Onyx I had access to had regular problems with various system hangs and lockups.