I second what Bo said. Although my retail system goes back to systems that have been around longer than some of the forum users (DTS2100), I am far more familiar with hospitality stuff. The point being that I do have experience in both. The current status quo of features and functions that people expect to see in a food service packages FAR OUTNUMBER the base features consumers expect to see in retail systems.
Unless you expect to tackle a very specific industry demographic (say for example, Pizzerias), you can expect the amount of features involved to accommodate the the basic restaurant formats to be 20 times the amount of work you put into your retail system.
What I've stated up to this point I consider to be fact, the following is just my opinion.
This market is over saturated with POS systems of all prices points and industries. As someone who has been doing this for closing in on 2 decades, I feel like the easy money left this industry 5-7 years ago. If you think you've got something great that you can offer, by all means go for it. I am not trying to discourage you at all, just saying this is a really bad time to enter the market that has definitely reach maturity.
However, the fact that your asking for a list of features people consider important doesn't lend itself well to you grasping the scope of a hospitality POS system (or fully understand the cost), since there are probably 50 features that any restaurant manager can tell you are standard-must-have's in today's market. A simplistic example of this would be splitting a check- 10 years ago, this was a feature that not all systems had or couldn't do well, and something like that alone might sell a system to a buyer. Now if you walked in with a system that couldn't split a check and do it well, you'd be laughed out of the demo.
But like I said, the days of adding a few flashy features and selling a POS system are largely a thing of the past.
Back to your question- the reason you're not getting a lot of feedback on this is because the important features required to sell a pos system are simply too many to list. It's like me asking what are the important features in a car? Well, that will cover a TON of ground and largely depend on what to with it.
Though it's getting less common to be able to do this, I suggest you download as many POS system demos as you can for the segment you want to serve and just research like a mad man.