I drive XL in Washington DC, Virginia, Maryland metro area. I am most likely to get XL requests Thursday night- Saturday night. Mostly college kids going to and from the bars and clubs. We have many colleges in this area. Also now that it is tourist season, I get XL tourist groups sometimes, and XL groups going to conventions/conferences. The other times I get lot of XL are to and from concerts and all kinds of sports games.Also sometimes get XL at airport with 4 or less riders but have a lot of bags. Get a fair amount of bachelor/bachelorette XL groups also.
ALso, sometimes extra tall riders or riders of "size," will order XL because they don't want to be crammed into a Uber X car, often a tiny Prius.
My area is probably a lot busier than yours, but if you do a little research you probably have enough opportunities to make decent $ driving XL. Especiaslly if you have an airport, concerts, sporting events, colleges, and a good sized bar or club area.
I drive a 2013 Dodge caravan. It has an economy, gas saving mode. If you buy an XL vehicle, I highly suggest one with a economy or energy-saving mode.