> [it] become[s] cheaper than gas heating within 11 to 14 years
This a no-brainer for buildings with high energy use. But we looked into getting a heat pump last year but it doesn't pan out because our house (15 years old) has a very low energy use and we would not recover the costs (about 20K euros after subsidies) for 20+ years.
With any luck, oil prices will rise enough to make that conversion worthwhile!
Your existing system will not last forever. When you have to spend money anyway that changes things.