This could be mitigated by just having people you don't interact with often in some meaningful way (for some definition of meaningful), they just get automatica

This could be mitigated by just having people you don't interact with often in some meaningful way (for some definition of meaningful), they just get automatically unfriended. As if you had forgotten about them. There's not hard cut _per se_, just that after the 150th, if both people don't interact, the relationship fades away...