This makes the most sense to me. Poshenko's trying a last ditch effort to either get Russia to go all in or pull out, either of which are better than this hunt-and-peck Putin seems to be pulling off. If Putin goes in, so does NATO, and if Putin pulls out, Poshenko has at worst more time to prepare and boost troop moral and at best can beat Russia back into the corner with nothing more than the opinions of other countries. It's a tricky gambit, but if he doesn't try this all he can do is lose.
I pity those people in East Ukraine who can't wait for this conflict to end. The rebels may have declared that they seek autonomy but that doesn't necessarily mean everyone agrees with them. They have the guns, Russian support, etc and all they need to do is tell the locals, "we've decided that . . . " Poroshenko should accept the peace deal terms so peace can be restored in Ukraine for the sake of those who don't want to be a part of the conflict.
