My reasons for being against offboard-only regrouping it are threefold; 1x fluff and 2x mechanics.
Fluff: the image of the broken necrons rising from the floor to rejoin the battle is a powerful one. In 40k a full 50% of all killed necrons rise up again from the battlefield, and only around 25% of the dead come back through the portals. Bringing one unit back per turn does not have anywhere near that level of "rising from the battlefield" imagery.
Mechanics 1: It makes things that should be a disadvantage into an advantage. Phasing out should be a generally bad thing, or neutral at best.
Failing an activation offboard should certainly not be better than failing an activation onboard. The main reason for changing the necron rule was so that we could get rid of the "lose all BMs when rallying offboard" thing, which I brought up in my summary thread a while back. All this change does is once again make being offboard better than being onboard, and that invalidates the whole point of the necron rule change.
Finally on this point, consistency is everything; I see no reasons that necrons offboard need to act in any way different to necrons onboard, other than the standard stipulation of not activating unless coming onto the board.
Mechanics 2: This is a
major nerf that completely changes the way the list works, and it's being pushed at the last minute before publication. It's much like the wraith change before the first edition of raiders, except this one effects the whole army in a HUGE way.
Such a fundamental change to the way the army works will require
years of playtesting, as it effectively throws out all playtests that have happened up till now.
Post Script:
My record with necrons stood at around 80%. Since the "no single monoltihs" change my win-record has been cut dramatically to around 50%, though admittedly from only a half-dozen games. I actually have a better record with my Dark Eldar recently ÂÂ
I am perfectly happy to playtest regrouping both on and offboard, and that is by far my favourite option.