I really don't know about this. When I was searching around various lighting websites today, I came across a few examples of 'hybrid' table lamps. They were roughly the shape of a mission style lamp, but they were as ornate as a Tiffany style lamp. I won't post any pictures here, because I don't own any, but do a quick search and you'll find lots of examples (or just press the following link: http://www.google.com/images?q=tiffany+style+mission+table+lamps)
To me, both styles are beautiful in their own distinct way, but they are very different styles. Tiffany style table lamps are ornate, with lots of organic details and flourishes. Mission style was opposed to such opulence, and therein lies its beauty. Putting them together doesn't feel quite right.
And yet... some of the examples seem to work quite well! I particularly like when the stained glass lamp shade uses simple geometric shapes (although one could argue that such a style moves away from the organic lines of a true Tiffany piece). Others may prefer examples that lean more towards the ornate. Either way, we live in interesting times, where there is such a rich history of table lamp design to draw from, and adapt to create a new aesthetic!
