Having rifted regularly in Beluslan over the past 3 months, I can say without a doubt that the majority, if not the totality, of these users are not having their leveling process blocked. 9/10 times I am the only Elyos in the region, and the only asmos I ever kill are the ones who harass me while I'm farming guards. The other 1/10 times it is someone else farming guards who I've never seen kill random asmos for the same reason.
In the time I spent in Heiron, I've only ever seen 1 asmo ever engaging in griefing - some Aethertech from the legion "Go Back to Sanctum." I've seen it all of 1 time in 3 months.
There's just too much else to do in game for such a thing to be entertaining, and the AP rewards for doing so are practically nil so there's no real draw to doing it.
That said, if it is truly is an issue the only thing opening up the rift would do is change the bottleneck location - not increase the frequency of it.