AFAIK, Vail owns Mt. Snow now, so perhaps they're intending to re-open Haystack as a feeder/alternative? Or do you think it was just a pick-up of some snow guns so they could use 'em at MS?
There's been a lot of speculation about this for a long time. I have written a couple posts here as have others. Mt. Snow has expanded snowmaking capacity in recent years and could probably make good use of the guns. But they could probably also make take a shot at integrating Hermitage/Haystack properties. Here are a few points to consider along with some of my thoughts.
1) Mt. Snow used to own Haystack Mountain. This was not a particularly successful endeavor. The terrain at Haystack is not great. It's OK but runs are not terribly interesting or long. The pitch can be inconsistent with long flats and runouts. When operated as a single resort, very few people skied at Haystack, even on the busiest days and even with discounted pricing.
2) Mt. Snow sold Haystack under the provision that it could not be operated as a public resort. I believe this is in the deed. It has since failed twice making it's viability as a private club questionable at best (although I believe that the most recent failure was more an issue with planning and strategy than with the model itself). I imagine that a sale to Mt. Snow (Vail) is the only way this mountain can be opened to the general public again.
3) Plans to integrate the two areas were always held up due to limitations on water access/supply for snowmaking. Mt. Snow has recently increased its capacity so perhaps the integration could work. The terrain in between the two mountains probably doesn't allow for the most interesting skiing although the town recently announced plans to open some of it for backcountry skiing, snowshoeing, etc.
4) For all it's failings, the Hermitage did build an impressive and luxurious lodge at the base of Haystack. This is one area where Mt. Snow has never had a reasonable offering. It's current lodges are utilitarian at best with some buildings simply worn out. They have demonstrated an interest in luxury offerings (the Grand Summit Hotel, some seated dining restaurants) but they haven't pulled it off in my opinion. Perhaps they could actually pull off a luxury offering by building on the Hermitage lodge and other amenities.
These are just some thoughts. No idea what may happen but there's certainly reason to continue speculating.