ReShade by itself is only a post-processing tool, nothing more nothing less. Adding other features than post-processing would bloat the code in the long run. Think it from a good software engineering principles perspective.
I also use RTSS for my frame limiting needs, I assure you ReShade's frame-limiting will not be any better. Also RTSS has custom Direct3D support for scenarios exactly like this.
But in the future, I would really like to create an additional module called "ReShade++" by collaborating with crosire. Not only frame-limiting, it would also include other miscellaneous features like clamping negative lod bias for D3D applications, disabling SetGammaRamp and SetGammaControl methods. It might take some time since I started programming this year, but I am getting there.
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