How long will the 2014 MacBook Pro continue to receive updates?

We can't say what will happen but generally for the past 10 years or so computers have been able to install new OSX versions for about 8 years (mentioned in a earlier post). For example, my late 2008 MacBook can run El Capitan but was left behind by Sierra. However, some features may not be supported in older computers if the hardware does not meet requirements. Things may also change since one of the requirements for keeping up with newer system requirements was being able to upgrade hardware (RAM, and sometimes drive) to run the new systems. Computers made in the last couple of years cannot have hardware upgraded. The push for needing more RAM has eased off a bit but if you purchased a computer that cannot be upgraded and you opted for minimal RAM to save money then you may find in 6 years you have a pretty slow computer. My 2008 MacBook runs fairly well with Mavericks because I was able to put in a larger and faster drive and upgrade RAM, otherwise it would be horribly slow.

You may be able to get an idea of how long Apple supports its computers from this article:

Vintage and obsolete products - Apple Support

Impossible to predict. But the latest OS still runs on Macs sold 8 years ago. I would keep that 2014 model. 🙂