Well the fact that weekend service is still a recent implementation as it started just last year, and we finally now have official confirmation that 30 min all day service to Bramalea is happening on weekdays starting at the end of April, its safe to say that Metrolinx can start to do way more now.
For weekend service all the way to Kitchener, it probably could happen late 2024/early 2025 if they want to either complete Guelph's 2nd platform and some passing tracks, or they would have to negotiate with CN to allow trains to run on the weekend past Mt Pleasant.
For full 2WAD to Kitchener I believe its just only going to be hourly while Mt Pleasant will get 30 min service. On top of the current projects, they would need to finish the plans they have for expanding tracks at and near DT Brampton before we see any sort of frequent all day service happening west of Bramalea.
The source for the service frequency was apparently deleted but there is an archive of it.
First phase of construction work to expand Kitchener GO Line train service kicks off
web.archive.org