1) Marketed web front-end for consumers
2) Confidence aggregation / metrics for both parties
3) Payment gateway / escrow service
4) Insurance and (sometimes) materials
I think we'll see blockchain tech replace the (2) and (3)'s here. With a decentralized ledger and some form of third party "notary", you can verify ratings for an incredibly small fee. Payment gateways and automated three-party escrow services are easy with multisig transactions, and can be converted to any other currency through coinbase, circle, or whatever.The (1) point could be replaced by an indirect revenue model, or by open aggregation apps.
(4) would then be put back in the hands of the actual service provider, where contractual liability belongs. A new business model could be born, where "Uber" simply has a nice phone app that references public blockchains to get you a driver, and sells insurance packages to drivers themselves. They wouldn't be locked down to just being an "Uber" driver, however.