That's what I've done, resize 6.5-284 Lapua brass and necked it up. I'm very satisfied with the results. I know folks are pushing this round to duplicate and attempt to surpass a 7mm rem mag, but I already have one of those. With Reloader 17, it's running 50fps slower than my 7mm rem mag.

My current load for my 7mm rem mag is 63gr reloader 22 pushing a 180gr berger hybrid to 2900fps using Norma brass
My 284 is using 52gr of reloader 17 pushing a 180gr berger hybrid to 2850fps using necked up 6.5x284 lapua brass.