It's not really a new caliber as it has been out since at least 2003 or 2004.
The bullet is a .270 caliber and most loadings are 90-115 gr that will do 3000-2650 fps in those weights. You occasionally see heavy bullet loads at 130 gr but I don't think that is the sweet spot for the caliber. The case is based off the old .30 Remington. While some people try to make it into a .270 Winchester "lite"....it really isn't. It is a good solid intermediate round that has better terminal ballistics capability than the 5.56. It's closest competitor is the 6.5 Grendel...the Grendel is a better round beyond 300 yards and many would say that the Grendel is the same as the SPC inside 300 yards.
No it is very unlikely that the caliber will be the new military round. In fact, I'd say there it is extremely unlikely that the military will select a new round anytime soon...more likely to keep incrementally improving the 5.56x45mm.
As you've probably read, it was developed with the help of some SOCOM guys and Remington had the first chamberings. The round has gone through some growing pain but it seems to have worked out now. The original SAAMI chamber specs were too tight and the old 1:9 and 1:10 twists were too fast. Gave too high pressures. The new SpecII chambering is better with the longer leade and 4 groove 1:11 twist barrels allow hotter loads (like the SSA Combat Loads). Remington still puts a large rifle primer in the round but everyone else is putting small primers. I use Starline brass myself.
I load my own 6.8 with Sierra, Hornady and Barnes bullets in the 90-110 gr range. H322 and Varget give the best results for me.
I think the 6.8 SPC will survive...it is being well supported by gun and ammo manufacturers. It is a decent round. It won't have the proplarity of a .30-06 or 5.56, but it will likely have a small but dedicated following for some time.
Here's my 6.8 SPC that I built about 3 years ago. I've been very happy with it and would not feel undergunned against any 2 legged predator and would confidently take any game that I would otherwise use a .30-30.

6.8 SPC AR build
- AeroPrecision Multi-caliber lower
- Stag/CMT M4 upper
- Badger Gen II TacLatch
- RRA 2-stage NM trigger
- VLTOR eMod stock
- WOA 18" SS SPR profile barrel and bolt
- PWS FSC30 flash hider / comp
- YHM front sight
- Brownells HK-type rear sight
- ERGO grip
- Magpul triggerguard
- MI low profile gas block
- YHM FF rifle-length quad rail handguard
- MI sling mounts
- EoTech 511 (soon to be swapped out for a 1-4x Millett DMS-1)
- PRI mags
- Now it also wears a CAA VFG and Surefire weapon light