Apache should support the PROXY protocol
To support reverse proxies passing through the originating source IP (for things like diagnostic logging, anti abuse and so on) Sympl should ideally support the PROXY protocol.
See https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt and mod_remoteip.
This may have to be a per-IP configuration looking at the Apache docs, or an overall system configuration. It would be nice however if it could be transparently configured.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information