I think the benefits of moving him at the draft are pretty significant.
1) any picks we acquire will be picks in this draft, not next year's draft. Which makes a big difference on the utility of those secondary pieces to us.
2) teams won't have started filling out their roster with UFAs/won't be fully focused on picking over this very thin UFA market and so will have more roster/cap flexibility and a greater willingness to make major changes.
3) it gives Patrick and Joe time to be fully prepared for UFA if they can have time to look deeper into what their options there are with a firmer understanding of what our future core looks like and what we need to fill (i.e. difference between a prospect who'll be at least pushing for a top 4 gig by seasons end, and one who is likely to just be earning their first callup by season's end; do we get a forward back in the ror trade?; do Soderberg/Martin/Sekera/Erhoff/Vermette re-sign with their current clubs?, etc.)
So I really do think there's a significant benefit to forcing the issue before the draft, unless negotiations are going better than expected and for a while real progress is possible...before things stall again, forcing the trade.
As for our D pool, I like it a lot to, but we really could use one more stud who has a higher ceiling than Bigras for me to feel convinced that our future on D will be sexy. I really love Bigras, and he will play with EJ if someone young enough to keep the job hasn't claimed it before Chris gets there; I still like Siemens a lot, his development has been messy and he needs a big year, but he's got nice middle pairing tools and has developed (even if it has been slower than we'd have liked); Gaertsen's exciting and could surpass Siemens if he keeps making big strides every year while Dunk slowly moves forward; and the other projects (Wood, Butcher, Corbett, Beaupre, Storm if he's still ours) are all interesting for their own reasons...but Bigras is the only guy in our pool we should feel confident in banking on becoming even "just" a top 4 guy. Though I do think Dunk and Gaerts can both grow into really nice Barrie partners, it's still going to take a while (quite a while in Gaertsen's case) and it's a gamble that they don't stagnate. To be well covered we would need a Zadorov/Morrissey type who can become even better than Bigras, so that we're still well set if only one of Siemens/Gaertsen can become an NHLer. Even if we do add a vet to give the kids time to develop at their own pace. That's why I see the need to add one more major young LHD talent in the ROR trade, regardless of what happens in FA.
Those reasons are not that significant.
Any pick we get wont really effect the immediate roster. we are not getting a guy like Zadorov and a 1st round pick. There is one benefit to having 2016 picks though. They can still be traded in the upcoming year. As an assist that's actually more utility right there. Whereas any 2015 pick is just turning into a prospect. I don't see a big difference between a 2015 2nd rounder and 2016, just a year younger. But like I said, I highly doubt we are getting a 1st round pick along with a guy like Zadorov. We're talking 2nd round and lower level talents. Not exactly something that should be a huge factor in this big decision.
Teams should know RoR is available. Nobody will have started to fill out their roster yet. With the new rules these teams can make plans A, B, C and D before FA even starts. RoR should be part of those plans. I'm not saying to make him available at the end up summer. And like you said, "very thin FA class". RoR will be a popular guy even if some other players have signed before it is known he is available. Was it hard to trade Spezza after the draft?
Patrick and Joe should be fully aware regardless. They, however, won't have a better understanding of the core. Sure, the defensive core would look pretty set, but then we put a hole in our forward core, which right now is set with Duchene, Mack, Lando and RoR. Either way we are missing a core piece. Waiting till FA gives us a better understanding of how we can fill that hole. Maybe we can sign a top forward, but not Dman. In that case we need to trade for a Dman. Maybe we can sign the top Dman but not forward. In which case then we would need to trade for said forward. Maybe we can sign both and then we can be really be open in what we take back in a trade.
Yes, Bigras is the only guy we should bank on to play a high role. Bleackley is the same case for forwards. But at least very solid group of Dmen with potential. The forward group is bare after Bleackley.
If we do trade RoR for a guy like Zadorov, what's your plan to replace RoR? Because that's a big hole we can't fill in house (other than Bleackley, but that's less likely than Bigras jumping into a top4 role). And free agency is, as you said, very thin.