The current unknown (at least for me) is knowing what we loose by flashing Harmattan with an aegis-free kernel. It is theoretically possible, though I haven't seen a list of what would be broken (probably OVI store, but the swipe UI should work, and Nokia apps maybe).
If we don't loose anything important with custom open kernel, then you just boot with nokia kernel whenever you install anything from OVI, and boot with other kernel the rest of the time.

But we need to know what works and what doesn't.