I don't know what we could reach within 1 billion od years. First we should concentrate on surviving here on Earth for next thousand of years because our current actions may well result in an extinction much earlier than that. Personally I believe that Planck accelerator could be built by Kardashev 3 civillization, eg one which could summon to intelligent use most of energy of entire galaxy. IMO such civillizations dont exist and probably cannot exist. Testing Planck energy interactions faces 2 major hurdles. First one and already an enormous challenge to accelerate particles to said energy is dwarfed by really unsurmonable problem of adequate *luminosity* of said accelerator. Just think about hopelessly small effective crossections for collisions at Planck energy. After all you are probing distances in range of 10^-35cm. It have been calculated that one attempting to collect data from 10 such collisions (to get statistically significant results) would need to accelerate *lunar mass* of leptons or 0.01-0.1 of solar mass of hadrons to said energy, all in a reasonable time. That assuming that he could keep a beam 1um (!) wide. So it is rather out of question. The best chance for such a device to be built is perhaps as a result of some sort of military arms race between 2 advanced Kardashev 3 civilizations. One could evaporate a planet by pressing a button over million of light years distance. Supermassive BH would be a power source, constellations of orbiting it neutron stars would be deflecting and beaming magnets/masses etc. Mind you, the risk of causing quantum vacuum phase transition (and destruction of entire Universe within Hubble radius) would be substantial during such experiments, so a large degree of recklessness is a prerequisite for those attempting it. So reckless civillization would probably finish itself off long before getting there. Practically I suspect that we might build 1 or 2 more generations of accelerators to get into 0.1 - 1 PeV of hadron energy (or 10-50 TeV for leptons). This will allow to investigate possibility of proton decay by electroweak process mediated by *sphalerons*. If no new physics, eg no new fundamental particles, are found meantime that is it. Great desert will be considered proven and Standard Model with all its shortcommings will reign for good. I cannot comment on "unconventional research". There is a slim chance that something worth attention is out there but it will rather go the same way like cold fusion research did. Mind you, conventional physics with string theories, multiverses and inflation is more and more religious like activity and insistence to work on it is a sign of decay of intellect. It is more and more unscientific. Peoples are insisting on beating a dead horse because they simply cannot admit that decades of their work are simply good for nothing. Peter Voit of Columbia University has something to say about it. Read his blog "not even wrong". Bright part of the picture is that a lot is still to be discovered in *low energy* physics. Who knows, maybe at picokelvins (10^-12K) and below matter starts to behave in such a way that we are not suspecting it even in our wildest dreams. These conditions most unlikely exist *anywhere* in Universe (and never did) if not produced by intelligent beings. Gravitational wave astronomy is another very promissing avenue. So even if high energy physics hit its end, there is still a lot to learn.