There are admittedly many issues with such a claim. We've seen objections raised on nearly every facet. However it is not super far-fetched to simply make 5000HP, given enough displacement, forced induction and a stable fuel. The material technology is there.
Referencing Nitro Powered TF cars and the like as a comment on it's practicality somewhat miss the mark when you acknowledge a few things.. they are limited to only 500CID and a specific blower/pulley combination. Yes, I typed "only 500CID" with a straight face.
Remember this is a hypercar, low production and won't be doing 15,000 miles a year commuting.
Then there are statements about the tires, and how they will hold up @ 348mph. Well, if you can find any place in the world that is not a salt-flat where you can even approach those speeds, it would be a legitimate concern. Even then, being my chosen sport is Land Racing.. you would do well to learn that GoodYear sells tires that are rated for 300+ mph with a healthy gross axle weight rating.
No, the biggest problem with a 5000HP car that will be running for more than a quarter-mile with any appreciable amount of throttle is simply managing the heat produced.
A spark-ignition piston engine making 5000HP at the flywheel, is wasting 2-3 times as much to heat. Heat from combustion, from internal friction, etc.
This heat has to go somewhere, and has to be dealt with somehow. This is accomplished via heat exchangers. They Veyron, an actual car, producing near-as-makes-no difference 1000BHP has 10 of them. For engine coolant, engine oil, transmission fluid, each of it's 4 turbochargers, etc.
The Veyron's W16 produces about 3000BHP worth of heat energy, only a third of which propels the two-ton behemoth down the road. That ~33% is actually fairly efficient for a spark ignited engine.. lets humor the 5000HP claim for the "Devel Sixteen" just a moment and pretend it exists AND that it is as efficient as the VAG group's halo powerplant.
It then has to deal with safely providing controlled cooling for ~10000HP or about 7.5 MILLION Joules/sec!
Of all the challenges involved with such a powerplant, this is the biggest and most unlikely to have been achieved for a road going car.