The questions of formats to support is a bit vague and perhaps needs to be qualified more carefully. Does support mean playing/editing in the timeline natively and flawlessly without need for transcoding/rendering? Playing/editing in the timeline natively but only at preview quality until rendered? Supported for import? Supported as a deliverable only?
I would add,if not already there already, the capability for delivering and playing back DCP packages. There is already an open source solution for d encoding DCP packages, so that should be leveraged. DIRAC is also open source so that should be available as a deliverable as well.
If we say we support a codec (natively) then we mean it will play fluidly in the timeline, on a properly specified machine. Obviously, some codecs need more powerful systems than others. ProRes, for example, which is an edit-friendly codec, will play on a lower spec machine than h.264-based Long GOP codecs, even though the bitrate of the ProRes material might be ten times that of the h.264.
But yes, it is complicated and there are a number of ways you could specify this.
Yes I know what you mean. However I think it would be best to be very clear about what "support" means in order to both gauge what people really need as well as to manage expectations.
Many people might find some tradeoffs acceptable. i.e. I wouldn't mind support for some only marginally popular codecs, like cineform, as import only or transcode only options, especially as licensing costs might be high for delivering or editing in this format.