I will be very surprised if touchscreen doesn't end up being closed up as one word (with no hyphen) in the vast majority of dictionaries within the next 25 years.
The Ngram chart for touch screen (blue line) versus touchscreen (red line) for the years 1970–2008 shows a persistent lead for the former, but that is before touchscreens on laptops became a standard feature:
(Note, however, that the results are artificially high for touch screen because—owing to a design decision in how to deal with hyphens—Ngram treats all instances of touch-screen as instances of touch screen.)
At the (U.S.) computer magazines where I have worked, our house style switched from touch screen to touchscreen at some point between 2005 and 2010, if I recall correctly. I'll check and see if I can nail the date down a bit more securely.
UPDATE: I found a word list from January 2009 that showed our computer magazines as still adhering to touch screen for the noun and touch-screen for the adjective at that date—but I'm sure that by 2012 we had shifted to touchscreen as house style.