I'm not trying to sound snarky, but I've been thinking this for a while and just want to throw it out there. Disney is a business. Like most businesses, they exist for their bottom line. I get that some people would rather stay offsite, or that they don't want to dine on property because it doesn't fit into their budget/ vacation style. That is their choice and their right. If they want to stay offsite for bigger, cheaper accommodations, to save money or to earn frequent stay credits, more power to them. But frankly, it's not Disney's problem. Disney needs to figure out how to fill the rooms they have on property and give people an incentive to want the above mentioned smaller, more expensive accommodations that don't earn frequent stay credits. Right now, they are offering FP+ and MB to onsite guests. This might (and probably will) change in the future.
If you want to make sure that everyone in your party has access to FP+ you know just what to do right now - book a room on site. Only you (or your extended family) can decide if FP+ is worth the price (which as of this moment is equal to the cost of onsite accommodations or paying to add on to someone's room). If it's not worth it to them, why should it suddenly become Disney's problem? They chose the Sheraton points over FP+. As we taught our children, life is full of choices. Everyone is complaining that there is no choice with the current policy and "testing". Of course there is. People just don't like the choices.
Reverse the situation... if Disney makes FP+ a "pay to play" program for those staying offsite, would you expect to be able to present your offsite hotel with a bill because they didn't include FP+ and you needed it so your family could ride attractions together?
This whole thing just reminds me of refillable mugs, staying offsite and being upset that you can't swim in the pools at the hotels you're not staying at and making salads at the Counter Service locations (after all, I paid SO MUCH for this vacation, so Disney OWES me X for free...).