if people ought to concerned it should be about pvp, but this is warmane for you. Shadowmourne exists on shop aswell in icecrown, but the server is still populated, so it's whatever.
PvE wise this will not affect progression of guilds in anyway possible. The dps increase is too small to complain about on one or two people. Rogues might gain 100-200 dps from it at times, not more than that. For Warriors this is not a big upgrade at all simply because of how heroic strike works on this server, it's not really blizzlike considering they fixed a long time bug blizzard retail had up until early Cataclysm which when you queued HS, your off hand couldn't miss as long as you had 8% hit.
This affects warriors in a major way as it plays with rage generation quite significantly and a fast off hand does not help at all in big rage bursts since it does low dmg. Ever since I got double glaives around 6+ months ago I felt my rage gen went down a lot compared to when I had a slow off hand, the dps increase is still there, but it's very minor unless you get blessed by the rng gods with low amounts of misses.
So again, having glaives on shop changes progress hardly in any way. It was expected this would happen when the server was launched a while ago.