Maya desperately needs its own native render engine, a new powerful one.
Arnold is not native, and it requires the user to buy the full feature set in order to be able to render animations (batch render, distributed render and so forth).
Maya users should not be forced to pay for third party renderers (V-Ray, Arnold, RenderMan... You name it), although some of them exist in their free version (well, only RenderMan does, and it's the better integrated one).
As it stands Maya is an incomplete package out of the box (at least for seasoned professionals, not so much for beginners and students, in their cases it's alright).
Modo, Cinema 4D, Houdini, LightWave, Blender and others, all have their own native renderer that makes these products independent from the third party plugins purchase and, as a consequence, a more complete packages overall.
So, my "idea"/ wish is to have a brand new Maya Native Renderer, modern, with all the most popular features (path tracing, GI, AI Denoiser...) and with the ability to choose between different render modes: CPU, GPU and Hybrid (CPU + GPU).
Now, this would be a killer feature!