I would like to see in the Visio 2025 desktop:
Support for 32 bits IDs in all the many functions, DropMany, GetResults SetResults GetFormulas SetFormulas and the U versions.
Improving the engine to support 10000+ shape diagrams and to still be performant (UI stays fast and responsive with 10000+ shapes on one page), to optimize the software for four CPU cores and more (as this has become standard now).
A webbased solution cannot compete with this, 10000+ shape complex diagram editing I expect to remain unusable in a browser for the foreseeable future.
Visio VSTO full .NET 5.0 and beyond support, a full rewrite of Visio from COM to highly optimized .NET 5.0+.