I have seen a live "band" (2 guys and some midi stuff) perform using a very old version of Cakewalk running a number of synth modules. I think this was when Cake was just midi sequencing. This was in the days before there were such things as laptops.... they had a state of the art 80286 computer. (about 22 years ago or so) They sounded really good. Speaking with them, I found out that they spent a week or more per song just programming the midi. Their cover tunes were immaculate.
Most laptops and a USB interface would give you what you need to run VST's live. I would keep the machine dedicated to music though..... keep it rock solid and stable. Last thing you want is a BSOD or a crash, glitch, problem in the middle of a song.
If I was planning to do a live show, I would burn the backing tracks to CD and or use a different computer to play the backing tracks. That would be much more stable and easy to manage than to trust X1 on a lappy in front of a live audience to perform flawlessly hour after hour, night after night. All it would take is one missed command to glitch the program and ruin the show instantly.
BUT.... having said that...I also witnessed 2 other guys recently (at a nursing home where I was working a service call) who were using a lappy running some version of Sonar, and they were in fact running it all live from inside Sonar.....even had BIG LYRIC VIEW up on the lappy screen.
So everything is possible....all depends on how you want to do it and how much faith you have in the lappy to run the program flawlessly.