The main challenge has been building a modern remote desktop protocol that achieves high performance but without requiring GPUs for each user and works on Linux. VNC is really showing its age, and X forwarding isn't really usable over the Internet. We are also using Yubikeys instead of smart cards, though I'm looking forward to testing some of the FIDO2 cards that are on the market.
One of our colleagues said something that really resonated with me "When you're working using our system it should feel like you're sitting down at a personal supercomputer". There are always more features to build, but the basic vision of being able to sit down at any desk with our Warpbox and connect to your virtual desktop within a few seconds is a really nice workflow.