We've uploaded the Lenovo ThinkPad P73 hands-on video.

Quick summary:

• A robust chassis, lid mechanism is solid; less fear of scratching the chassis (the design looks and feels built and ready for work, rather than as a fashion statement, which some other manufacturers have started to apply to their workstation line-up).
• A range of upgrade options from Lenovo (upto RTX5000, 128GB RAM, etc looks great on paper). Upgrading increases the cost quickly (you'll need Core i7-9850H upgrade to support the RTX 4000+ cards). It's useful to start with "what problem I'm I trying to solve" and work out what you need the laptop for (check the hardware requirement of the app & upscale slightly for future versions if needed), rather than checking out the max spec (tempting as it will be, the cost can build-up quickly / idea around diminishing return applies).
• A decent array of user-serviceable upgrade options (4x RAM, 2xM.2+1x2.5"). This is expected from a workstation laptop - it's good to see it being retained. 
• Upgrading options increase the cost quickly (you'll need Core i7-9850H upgrade to support the RTX 4000+ cards). 
• The RTX 4000/RTX 5000 cards are Max-Q cards (rather than full performance cards). Still very fast. Some reviews online (e.g. NoteBookCheck) seem to note a limited available thermal head-room; that GPU, as well as the chassis, could be better cooled (there may be benefits to focusing the upgrade asymmetrically - e.g. either higher CPU spec + mid GPU or mid CPU + higher tier GPU - so cumulatively you still have some room).
• The chassis hopefully could receive an update to be more modern (of course, a thinner / lighter chassis would normally have some functionality trade-offs - so we suppose that you can't have it both ways).