We currently have this issue in OSMC.
OSMC has a configuration utility known as My OSMC, and we have always wanted it to look the same across all skins. This has been hard, and in the past one of our add-on developers has (quite hackily) injected the necessary fonts in to the Font.xml that the skin provides. This has worked well since February 2015, but it means we need to trigger ReloadSkin, which has a race with Skin Shortcuts sometimes and can occasionally cause a crash. This is usually when Kodi is updated (and script.skinshortcuts rebuilds the menus).
For Krypton, I plan to allow add-ons to load their own fonts in OSMC. They just need to use a 'Fonts.xml' like a skin would, but the limitation is that the fontset id must always be Default for now. But this approach is better as it means we are not modifying skins, which can cause issues when they are updated.
My patch is here:
https://github.com/osmc/osmc/blob/krypto...font.patch It lets you have different fonts for 720p/1080p etc.
I will refine it for our Krypton release. I suspect it's too hacky to even consider for upstream, but I don't know enough about Kodi's skinning internals. For OSMC however, it is suitable: it means that My OSMC can always rely on its fonts being available, regardless of the loaded skin. This lets us have a consistent visual appearance and not have problems where people say they can't read text etc.
It's good to know we are not the only ones who have wanted this option. I wonder if it can be adapted to serve a more general purpose.