Forgive my ignorance, but I don't know where to look for any information related to specifics of what the HD500x will actually be capable of that the 500 doesn't do already. I'd be keen to read the info about the HD500 chip being discontinued if anyone has a link? It looks like the 500x may be a rev2 driven by the old chip being end of life.
L6, Boss, TC, everyone, take note - Guitarists will pay the big money for the product that can do the best job. If the chips you want to build in are too expensive, think about the G-system's huge price tag and have faith that your customers will choose your product if you can promise things they want, and deliver. Other technology advances so quickly, and musicians are largely being left in dust. They must have a hard enough time getting everything done on time and working solidly, let alone paying as much attention as they already do to their consumers, which is awesome commitment. A friend of mine used to be the product manager for L6 for Australia, and until a few years back they were only doing a few 100k in Australia. After he was done they were doing a few million, and he gave me some crazy stories about what goes on to get the products conceived, manufactured, tested, revised, manufactured some more, packed, shipped and priced at your local store. All up it's impressive business especially in this climate, and in the grand scheme of things, the product is amazing.
I love my Line 6 gear, have done for years, and kudos to everyone there! What I was getting at is, I'm hoping I can use more than 8 effects. If you're trying to craft complex tones, it's extremely easy to use up 8 effects on a single channel, let alone two. A nice guitar path might be Amp > EQ > Screamer > Wah > Modulation > Reverb > Delay. There's 6 blocks taken before I get to my vocal path, which needs a compressor/EQ/Reverb for what I'm doing. Now I've gone over 8 blocks, and I haven't got to my crazy effects yet (Think of sounds from bands like Ratatat).
With the Boss unit or an Axe-FX, I'm never worrying about 8 effects blocks being filled up. If you read the manual of the HD500x available on the Line 6 site, it still tells of 8 effects blocks.
http://line6.com/data/6/0a06434c6fb051e03e8ab63dc/application/pdf/POD%20HD500X%20Advanced%20Guide%20-%20English%20(%20Rev%20A%20).pdf
(Page 3.1)
"2x the processing power" of the HD500 could be a misnomer for any number of things. Dropping in a more powerful chip doesn't mean you have access to 16 effects blocks and 4 amps simultaneously, unless the rest of the unit has been tweaked/programmed to support it. At least that's my understanding!