Sounds like the classic chicken or egg dilemma, need success story's/cases to deliver prove to justify development of a system, also need a working system (before that prove) able to generate such cases. How to get the one before the other?
Also agree many would be reluctant (me included) to having risks of not being paid, that's why the system would need to work so well (for majority of people) so that it can survive unavoidable intrusions or bad intentions (maybe ability's to work whit insurances are possible?).
The thing is, people with bad intentions will always be there, it shouldn't be an argument against creating something. Besides, regarding security, sooner or later things get taken from the servers anyways, just like it happened on Ts , and then it gets on the dark net to collect download fees. Such things are unavoidable, but what keeps standing as a real use and value are services/interfaces that are well designed and give lots of good and easy to use tools for those hoe are willing to develop and build towards the future. It is probably also the best means to get a large and loyal user base of this type of people.
Regarding the market size, the (hypothetical) system would be something that is able to streamline how projects get done, and potentially make market bigger (more projects initiated). There is probably no way to be 100% sure (before testing) how many would make use of such system.
We can however get some statistics on how many CG related projects where launched via crowd funding (e.g. games, short animations, VR applications, apps, etc.) And then draw estimates/conclusions on how many would probably move to a same system including ability's to project manage and collect recourses before getting to the crowd funding round.
The main selling point of the system is this connection to recourses early on, making it more attractive to built projects via this system.
To close off, consider this, all things already exist but the direct links between them are missing. We have crowd funding platforms and online project management systems and large repository's of recourses, however no one has managed to marriage these three things into one good functioning whole.