By all means do so. But we have found that adding properties because users think they would be nice has not been successful. What we have found to work is at the request of device manufacturers and/or application developers. They know what they need and what they are prepared to implement. The last Camera upgrade came like this, a group of camera manufacturers and application developers got together at AIS a few years ago.
As far as I know neither of these suppliers are at all involved in ASCOM, by which I mean that the driver authors don't have any sort of presence on the ASCOM-Talk forum. I may be wrong, they could be there incognito.
In my opinion you will be better off persuading them that you need this. We will be happy to work with them to extend the specification.
We need some sort of buy in from hardware people and application developers that they will use new functionality, not least in order to implement what they really need.
There is something that is available now in the ASCOM specification - the Action method and SupportedActions property. An Action could be added called "Offset" with a parameter of the offset value. It would return the current offset.
All implementers could implement this now and if they all agree to use the same Action name it would work with no changes to the ASCOM specification. If it proves to be useful it could be added to the specification.
The thing that worries me is that the point of ASCOM is to define a common standard for all devices of a particular type. Having a multitude of different properties that have to be used differently depending on the type of device that's being used rather defeats the purpose of a standard.