Recently, while administering a large board running IPS 4.x, I saw that there are a lot of performance optimizations already in place which is great. I also saw a few instances of front and back-end performance issues, and in some cases, outright crashing; one of these boils down to 2 things:
Embedded iframes (like tweets) do not use the deferred loading=lazy attribute, so on topics with many embeds, pages slow to a crawl or outright crash (esp. Apple devices)
Embedded iframes seem to point to an iframe loader as a sort of internal proxy, which increases load on the server, particularly for large sites, probably predating loading=lazy
I have implemented this optimization here: https://vbresults.com/downloads/speed-optimizations-ip-community-4 — and the IPS team can merge it into the core if they see fit. I'd like to expand on this by dis-intermediating the iframe where possible, but understand there are other reasons for it like the layout.