Like I say, I'm not sure what the performance impact is without trying it. It saves some, it costs some. Should be explored. In any case if I follow 500 people, which relays am I asking this of? My presumption is that I still find those 500 people's write relays and go ask them, which means I wouldn't be "subscribed" to many of these relays, or I'd have to sign up to a lot of relays, or else relays also have to shuttle from other relays.