I started this project wishing to build the station around a pen form factor with USB PD as the power source. However, as I started using the perfboard prototype built around the USB PD idea, I realized the RT series of tips really are best used for stationary soldering and a traditional table top station form factor makes a lot more sense, let me explain. The RT pico line of tips are toothpick-thin and are great for micro soldering under a microscope, and I don't see myself ever doing that kind of work "in the field". The RT Micro line are great for general soldering, but the TS80P already exists and the type of tips available for the TS80P is growing steadily. The RT Ultra line might be good for soldering copper pipes in the field, but that seems like a pretty niche application.
The table-top soldering station form factor is not without merits, for example effortless ESD safety, possible use of high quality silicone handle cable, rotary encoder for temperature setting, easier ergonomic handle design etc.
Going forward, I'll design the PCB of this soldering station around a traditional desktop form factor, and if I ever change my mind and want to build a pen sized RT soldering station, I'll just redesign the PCB for a compact size, and most of the heating control code should be reusable anyways.