The only ones that care about the Spider name also care about Glenn's opinion. I for one couldn't give a .... Amazing amp and in my own opinion, far more than just a "practice" amp. If people aren't coming to your gigs in the numbers you'd expected, it has nothing to do with if you used a Spider V MKII amp or not. A mirror will help you find the real fault. Besides correct mike use, one can always go the full digital recording route via USB.
However, outside the update to support the Relay G10TII, I suspect that there's not much further refinement to be added by firmware upgrades to the Spider V series. Line 6 did an amazing job with the big 2.0 update bringing MK II to the market.
I've wondered if Line 6 might release a new Spider VI (6) eventually that has the modeling technology from the Pod Go, but it's also possible to set the Spider V and V MKII amps as just a clean full range speaker, so perhaps that would eat into the Pod Go market that would pair well with a Catalyst amp.
Only time will tell! But I've seen absolutely no "discontinued" notices, only the occasional "out of stock" only to see Sweetwater, Guitar Center and also Andertons across the ocean get them back in stock.