Leveling the playing field, at least a bit. The problem is the Left loons move to red states and vote their same errors...they hardly ever learn.
This is my concern as well. Full disclosure; I am a rare small-government, tea-party type living behind enemy lines in the people's republic of NJ, and this will only expedite my exit from NJ. Unfortunately - as you stated - many of the hypocrites on the left who usually advocate for higher taxes (just not for themselves) will also move to lower tax, relatively reliable Republican states and erode the margin of electoral safety, turning the states 'purple'.
I will take a financial hit from this SALT limitation in the tax bill, but I am willing to bite the bullet in order to see more pressure put on the state governments in NJ, NY, CA, IL, etc. to do what they should have been doing in terms of legislating some tax relief for the tax-paying producers in their respective states instead of soaking us in order to support the masses who rely on the tax-payer funded handouts in exchange for voting dem.
I just hope it doesn't backfire by shifting the electoral map against us as it has in Colorado and Virginia for example.