AFAIK pas2js doesn't fully support the full runtime library yet and i think the language isn't completely implemented. IMO the wasm target will be more interesting and was merged into the main branch earlier this year, though i don't know how usable it is.
Either way those are things that allow you to use Free Pascal code in the web on the client side, but they aren't really "Lazarus" things. Once the full RTL can be used via pas2js or wasm, it could be possible to make a web-based backend for LCL but that would feel kinda alien as you'd essentially be embedding a desktop application inside a web page.
It is also possible to make new form (object) designers for a new type of form (object) that acts more like a Flash page or something like that, but that would require a lot of work. On the other hand it might make making mobile apps better too.
