Is there any estimate of how many active kdenlive usere there are?

Any idea how to count them? ;) We cannot even count the downloads due to the distributed repositories.

Is it possible to create a mechanism when kdenlive is first used to voluntarily submit a count with some details (version number date etc) and somehow collect the counts?

Sure it is possible. That's not the problem — but many people do not like programs reporting something to a website, be it only for a counter.