Looks like this filter size limit is currently hardcoded in Strfry. if (buf.size() > 65535) throw herr("total filter items too large"); https://github.com/hoytech/strfry/blob/32a367738c6db7430780058c4a6c98b271af73b2/src/filters.h#L38
I wonder if it isn't better to send the notice, but just crop the amount of filters to the max limit of the relay. But I don't know.. I feel like the filter array already allows the relay to run one after another instead of all at once. In that case, it might not make sense to put limits in size. An OR in 2000 pubkeys seems better than 2 subs with 1000 pubkeys each.