I mention this Lenovo laptop as I think you can change its firmware to CoreBoot, and it has a Haskell CPU, which for Free Software is quite modern and powerful. It is MilSpec, so tough, and great for upgrading, including swapping out the display for a 1080p IPS panel.
If you get one running with CoreBoot, you could install a GNU Linux Operating System, for example the forthcoming KDE neon, and replace the Linux kernel with GNU Linux-Libre.
There have been some claims that swapping out the flat touchpad on the T440p and replacing it with the T450 touchpad can potentially damage the screen.
The reasoning is that the T450 touchpad has physical buttons (which is why you want that touchpad), but as these buttons jut up, if the laptop lid is closed particularly tightly, then they might press into the panel, causing damage. The way to prevent this is to add some plastic bases to the top of the laptop, as described in this video here:
Whilst on this topic, prices for the T440p seem to have edged up a little, particularly for ones with higher end parts, so it is worth checking the bidding history on purchased units to see what the market is like.
One other potential pitfall: a lot of the panels that are sold are listed with the part number that you want. The panels will fit. They might even be IPS panels. The problem is that they are "compatible with" rather than the genuine panel. For example, you might be paying extra for an IPS panel made by LG, but the item will be listed as compatible with that panel, so you might be getting a Mickey Mouse IPS panel that fits, rather than an LG one.