I am all for having multiple staging trees that get MERGED into one upstream tree.
Let me make it simple, no out of tree drivers. I am not supporting, maintaining or submitting drivers that are not in the mainline DPDK product. If you want me to submit drivers, then they should go into the mainstream. Developers: Want to be able to make changes to core infrastructure during merge window and fix all the related drivers. For many devices, developer wants to be able to submit a driver and have it fixed by others in the main tree. Vendors: Want to be able to extend, change, and enhance the existing DPDK tree and then build an application with that. It is a increase in technical overhead to merge in drivers from multiple sources.