You wouldn't want to do this for streaming traffic, as it could negatively impact the experience of the device with the strongest coverage. But you could do this for traffic that has lower performance requirements.
Paid prioritization has existed over the course of the entire Internet. I happens every day- and it is known as peering agreements. Would you characterize the history of the Internet so far as "stifled growth"?
Just how to preserve this unnatural state of affairs is what is being debated. If we don't understand this fact -- if we create laws or technical standards that favor one type of packet over another -- we risk foreclosing all sorts of interesting and valuable applications in the future that no one has even imagined yet.
So no, I don't think it's a good idea to promulgate standards that work well with transient messages and datagrams but not streams. If that's true of LTE Direct (and I'm not familiar with the spec, so I don't know if it is), then that's a problem. We've already baked that behavior into the architecture of the Internet itself, and it's only going to become a bigger issue as time goes on.
I have absolutely no faith that the government is capable of responsibly managing this ecosystem.
Let the nerds work. Do not bring regulators in whenever architectural decisions need to be made.
Say you're a mobile carrier in the not-too-distant future. Lots of your customers are addicted to the hottest new social network in the Valley, FaceFlix. Trouble is, you're catching hell from both sides -- your customers are complaining about sluggish performance, and FaceFlix is complaining about inadequate bandwidth. What's your path of least resistance? Do you spend money building out your network, buying expensive chunks of spectrum at auction and erecting new towers all over the place? Or do you choose to make money, charging FaceFlix to drop their competitors' packets into the bit bucket? It will seem like a no-brainer from your point of view, and that's why paid prioritization is a bad idea.
It just sounds like a recap of the apocryphal story from the early telephone days, where a local undertaker was said to be bribing the operator to reroute calls away from their competitor. Why is that behavior suddenly OK this time around, in your eyes?