I have to had a TrackPoint (so no Dell for me), and I like smaller, 13 inches laptop. From what I have found, 16 GB is the maximum that exists.
Some Dell models do have trackpoints. for example, http://www.dell.com/us/business/p/latitude-e5570-laptop/pd
Dell XPS 15" (9550) goes up to 32GB - upgradable after purchase with 2x memory slots.
e:
Links for the 15" with 32GB:
Dell Australia: http://www.dell.com/au/p/xps-15-9550-laptop/pd?oc=z510896au&...
Dell USA: http://www.dell.com/en-us/shop/productdetails/xps-15-9550-la...