Hi Yetkin.

Are you looking for a place to suggest an idea that someone else could make (or check if someone already requested it)? or for lists of existing suggestions from other people that you could work on implementing yourself?

On Phabricator there is https://phabricator.wikimedia.org/tag/technical-tool-request/ (that's probably one of the better options, for a place to write down your ideas for someone else to possibly work on).

On Metawiki there are the various https://meta.wikimedia.org/wiki/Wishlists (the Community Wishlist 2019 concluded recently, and contains many great ideas that someone could work on moving forward (whether code or research/organization/etc): https://meta.wikimedia.org/wiki/Community_Wishlist_Survey_2019/Results )

On Wikidata there are many existing requests on the talkpage at https://www.wikidata.org/wiki/Wikidata_talk:Tools

Some other wikis maintain lists in various locations, depending on the scale/scope of the idea (e.g. gadget/userscript request pages).

Generally: There are always more good ideas than there are people available to implement them, so there's never been a simple way to go about it.

Hope that helps.