You don't have to be a MMA member to start implementing MIDI 2.0 products. MIDI standards are available for free and require no license fees or royalties. MMA membership only gives you Manufacturer SysEx ID for proprietary SysEx dumps, the right to use the MIDI logo, and participation in private meetings and events.

USB-IF has their own membership and licensing policies which MMA does not control. It just so happens that USB hase become the protocol of choice for wired connectivity, so MI companies have to follow their users.
Ethernet, RTP-MIDI (AppleMIDI) and AVB/TSN (MILAN) come with no license fees or royalties, so these are probably more attractive in terms of development, testing and implementation costs for the UMP protocol products.

MIDI-CI specification does mention "New 2-way UART" - hopefully the idea is not abandoned and industry standard differential bus, like RS-485, M-LVDS, or Ethernet over twisted pair, would be used as a physical layer.

Practically limiting devices via cables to hosts MIDI 2.0 with USB ,for now, pushes creators of MIDI devices into a $6000 USB vendor ID application + the $600 annual membership for SYSEX that is now mandatory for MIDI 2.0.

First, MIDI 2.0 products that implement and support Profiles and Property Exchange can be done on 5 PIN DIN or any other existing MIDI 1.0 transport.
So there is a whole range of MIDI 2.0 products that take advantage of MIDI-CI, Common Rules. for Profiles and Common Rules for Property Exchange that don't need UMP or a new USB-MIDI 2.0 driver.

Second, a small developer certainly does not need to join the USB IF or the MMA. The MMA is working with the all major OS developers and they will develop and release class compliant MIDI 2.0 drivers. The only thing we can't say is when, but you can certainly ask and request that Apple, Google and Microsoft support MIDI 2.0. We certainly have!
Most music companies will rely on those class compliant OS USB drivers. Once the USB-MIDI. 2.0 specification is adopted, it is also made available to the public (just like MIDI 2.0 was) and if you have the capability to write your own driver to add more functionality you could download the spec and roll your own driver.
But again most small companies and devices just rely on OS class compliant drivers so end users don't have to download and install anything for the product to work.

If you want an MMA SysEx ID for a commercial product, it is $240 a year to get an MMA SysEx ID, not $600 which is the cost of full voting membership.
Development and commercialization of a MIDI project is easier than it has ever been. Everyday there are examples of Kickstarter and IndieGoGo projects where small developers raise thousands and thousands of dollars based just on a cool idea for a MIDI project.

If you don't think that your idea or product is worth $240 a year for a SysEx ID, then just give it away. If you want to just innovate and not sell products, there is a range of SysEx IDs available for research and non-commercial use. These have always existed and are documented in the MIDI 1.0 specification.

The MMA tries to respond to the needs of both our corporate members and the entire MIDI community at large. We think once people really understand the implications and possibilities of MIDI 2.0, they will see that it was designed not to raise the cost of developing MIDI 2.0 compatible products or the cost of those products to end users.