I would love gg.deals to be included in the third-party links added to Steam game pages by the Augmented Steam, but not sure if that will happen since it's currently developed by a rival service.
Either way, adding something like that via any userscript or extension would probably require an API request with the Steam game id to the gg.deals and getting back the gg.deals game url. Also, an API could provide a way to show current low/historical low on Steam pages like SteamDB extension already does, but with more stores. Is that currently possible/planned?