Er, Craglorn in VR10.So you want a solo player option on a MMO.....
4 man instances are private, but I believe the reason the rest is that way is to stop insane farming.
If they gave an option for any instance to be a 'private spawn' expect there to be little to no loot.
Also, I thought all Craglorn instances were private, so you do have that, but you have to wait to V1+