I think the Pats will eventually have Edelman as the 3rd QB, as long as either KOC or Walter steps up (Hoyer to practice squad). Whether this happens before the season starts or at week 8 depends on how KOC and Walter are doing.
I suspect that the Pats see a lot of potential in Walter, and how he works out will probably determine whether we drop a 3rd QB before the season starts or mid-season. If Walters seems to learn well in our system, I think we drop KOC the moment BB thinks Walter is ready to be #2.
There is a lot of incentive to make a determination on Walter quickly because if he doesn't work out and BB is ok with KOC as #2, you can drop a 3rd QB before the season starts to make room to keep an extra roster spot open for this talented team.
Problems arise if BB is not happy with either KOC or Walter as a #2. He'll be forced to carry 3 QB's to develop or find a solid number 2.
Either way, I figure by season end Edelman will take up WR, QB3 and Wildcat QB slots in one, inexpensive package. Heck, his salary is probably so low, it won't even be reflected in the cap
If this kid works out, he'll be a huge value saver for the Pats for 4+ years. This draft class could be the foundation for the new Dynasty.