Already tried this and it didn't work.
Over 20 years ago, in a different life, the company I worked for at the time tried using a touch screen in a tank. Although it made a terrific demo at the various Army conventions, it really was a bad idea in the field. The reasons why?
1. At a static display in the convention hall, hitting the appropriate area on the screen was no problem. In the field, with the tank bouncing around (believe me, tanks bounce around) hitting the appropriate area of the screen became a real problem. If the area of the "button" was to small, it was possible to miss it completely or to hit more than one at a time in which the program got to make the decision as to what was pushed. If the "button" was made larger, more screen real-estate was taken up so that a smaller amount of data, etc. could be displayed.
In times of distress, fairly common in a tank, trying to hit a button on a screen with it bouncing around, took the operator's attention away from what he was dealing with. This is a bad idea in a tank and in an airplane. There will be times that an airplane will be bouncing around, etc. and the pilots will have the same problem.
2. Having the displays change unbidden caused confusion and problems. If the operator looks at the screen expecting to change the type of round being fired and instead he sees an engine diagnostic that requires his attention before allowing the round change, a really big problem will occur. Same with an airplane.
3. The lack of a tactile response and the delay the computer gives while deciding what area has been touched caused some problems. There were main screens that the crew would be using most of the time. They got used to the position of the touch areas for those screens and would not necessarily look to see if their touching of the screen got them the response they wanted. Also, as they got use to the screens, if a particular screen required a second screen for additional information, they would not necessarily wait until the computer(s) brought up the second screen before touching the area wanted for the desired response. Once again, a potential problem in an airplane.
4. The thing that REALLY killed it for use in a tank was when we tried using arctic gloves on the screen when in the field. Nothing worked because the gloves were so big and bulky. It required removing them in order to work the screen which is not at all acceptable to the Army. This probably is not going to be a problem in a cockpit.
For these reasons and many of the others already stated, the use of a full screen in a cockpit may be a real bad idea. It looks great in a static demo but in a real situation in a cockpit it may add to the confusion at a time that it is critical that appropriate decisions are made and executed.
