Technical consultancy and code review services

Hey guys, quite some time I was wondering why there is no good platform of freelancer consultants to hire consultants on different technical topics.

There is upwork (and similar platforms) to hire a developer, but this is different.

Just an example: Your company is adopting reactive programming, but no-one in team has an experience. That is quite a different world comparing to traditional programming, and after some time that you develop the MVP, you can enter the platform and find freelancers who are very strong at topic and you can hire them to review the design and code over GitHub.

What do you think? Would this be useful to you?