Currently, Quark runs rather well when only installed clientside, but there's a few issues where it crashes or shows options that don't work.
For example, trying to craft a birch chest will crash once you mouseover it, and the "quick stack" inventory button doesn't do anything.

This isn't a problem per se, Quark has config options to disable all the features causing issues.
However, client- and serverside options aren't separated or grouped together, making it difficult to find out what's what.
I would suggest adding either a config option to disable all server-side requiring features, or automatically probing whether the server is running Quark or not and disabling them automatically.

I don't know if Quark on only the client side is officially supported or not, but it works almost flawlessly out of the box already so I'd assume it'd be a small step to "full" compatibility.

Minecraft version: 1.10.2.
Quark version: Quark-r1.1-70.jar
Modpack: Age of Engineering

+1

This has been added in recent Quark versions (as per this tweet) so I guess this can be closed now. I was waiting for Vazkii to close it but I suppose it doesn't matter.