Comes up every now and then, TL;DR no, getting that right would be exceptionally difficult and is way out of scope of the project.
We can't just take the rendered image and make it bigger, we'd need to make the application window bigger too. This alone would already break a million games without targeted workarounds as well as extremely good understanding of every little detail on window messages and relelvant GDI APIs (which we don't have) since games can reasonably assume that their 640x480 window is actually 640x480 and not 2880x2160 or something, but even if that worked, we'd also have to remap all mouse input etc as well.
On Linux, Gamescope is the way to go to run games at weird resolutions.
which makes the game show the HUD big like the small resolution, but the rest of the rendering is big resolution.
This is also not possible to do at all in a generic way, we cannot know when a game does "normal" rendering as opposed to drawing its UI or doing internal computations that must happen at a specific resolution to be correct, it all looks the same to us. You're looking at manually patching shaders etc for thousands of games if you don't want to limit this kind of functionality to the most basic of D3D8 / early D3D9 games.
Probably D3D8 would be enough, D3D9 and higher mostly allow any resolution themself. Some older games arent smart enough to just pull the resolution list from gpu driver and offer these resolutions. So there is e.g. NFS 4 High Stakes which offers only 4:3 resolutions which makes no sense with a widescreen patched dll and exe.
But ok then I will use dgvoodoo 2 for these games, because dgvoodoo 2 can do it for any game.
Nothing extracted yet.
Can we add upscaling like dgvoodoo2 etc offers?
So that we can set a target resolution and choose between different scalers (lanczos, spline, bicubic etc)
with dgvoodoo2 you can then even set the ingame resolution to small to prevent small HUDs for games which dont scale the HUD with res, and the dgvoodoo resolution to "desktop", which makes the game show the HUD big like the small resolution, but the rest of the rendering is big resolution.
Some older games also dont offer big resolutions and then you would be forced to play it in lower resolution.
So: Upscaling would be nice addition.