The Boss 302 crate is an updated/improved original Boss as you say. I think you are correct that the new (coming) Boss (formerly Hurricane) will be an SOHC (possibly a 2-valve in the trucks), but I doubt that the 5.8 will be a stroked 5.4 modular.
It is conceivable Ford could do a 5.0 as a stroked 4.6 mod in the interim (like the Saleen PJ -- dunno) but the 5.4 is as stroked as the modular motors will realistically go.
I think the new Boss (ne Hurricane) is an all-new motor
with bore spacing roughly analygous to the 1960s FE-series and will likely debut in the F-series on '08 and, we hope, in a Boss Mustang in '09 as a 5.8 SOHC to take on the Camaro LS2 and then as a 6.2 (or 7.0L
to take on the Challenger and Camaro LS7.
The bore spacing of the present modulars (3.55") has the displacement fairly tapped-out in the highly-undersquare 5.4. I imagine siamesed and cross-drilled cylinders (like in the new 363cid Boss 302 crate -- unrelated to the coming H/Boss) could conceivably push modular bore just a bit further to get to 5.8 with the present 5.4's crank, but that approach is not likely a realistic option for a production motor (as opposed to race applications), so I'm highly skeptical that either the 5.8 or 6.2 engines coming along would (or realistically could) be on the present modular base.
Sure is confusing, huh?