P1 hits the sweet spot of thin AND pro. Same size as the X1 Extreme series, but geared toward business users. You can actually open it up and do some upgrades. RAM up to 64gb, up to a xeon processor, and the 1st gen is able to include nvidia quaddro gpus.
Ah yes, the P1 is an excellent machine and still manages to stay pretty thin. Its definitely an outlier of thinness in the P-series though, but is absolutely one which does not fit with my earlier comment of the P series being a bit thicker.
FWIW, most of the T series also have a good number of FRUs (field-replaceable units, what customers can easily swap out). Some models, especially the "s" versions, will have some soldered RAM but often the non-"s" versions will allow you to swap out both sticks. Wireless chips and SSDs are user-replaceable. Internal batteries are held in by screws and not glue so they're easy to replace when they age. Pretty easy to work on overall. My T460s is over 4 years old and still going strong.
