LO's Resident Time Lord
Not necessarily. There are some common elements, such as Inquisitorial Storm Troopers. Give them a boost somehow (new wargear, better stats, cheaper, whatever), and those are the first troops choice.It would have to be a huge book to do all three ordos justice. Not saying it isn't possible, but it would be tough. There's a good chance that something really cool will get overlooked if they try to do all three in one book, although I do think this is probably the route they will take.
Prepare to be "streamlined" or "simplified"
Then, have Grey Knights, Sisters, and Deathwatch Kill Teams in the "Elites" section, then, in the HQ section, have a canoness, grey knght hero, some equivalent for the DW (librarian?), and then an "Inquisitor" entry with sub-entries for specific types (OH, OM, OX).
Now here's the kicker: Make it so that ordo-specific HQs make the chamber militants "troops" choices in that army. So, for example, an OM inquisitor means Grey knights can count as troops AND Elites.
Granted, that's just troops and HQ, but that right there will allow current =I= players to pretty much reproduce the same lists they have now, aside from certain specific WH elites and fast attack choices. Now there, I admit there's a problem. GW's either going to have to create some new OM/OX counterparts to, say, seraphim, repentia, flagellants, etc., or cut some of those from the new 'dex. Probably both.
So yeah, some of the WH units may go bye-bye, but most of these are units that people have trouble making work now anyway. The CORE units, I predict, won't be going anywhere. If anything, they'll be easier to use, and some of the popular heavy support choices, such as the exorcists and land raiders, well, the developers would be fools to get rid of those