What am I missing here? There’s not a whole lot to a rocket motor. Couple turbo-pumps to supply the fuel and oxidizer at the phenomenal rates at which they’re consumed, powered by the same fuel source from which they’re pumping, and a reaction chamber, and an exhaust bell with a heat exchanger. (And ignition if not hypergolic) I mean look at that unit on his table there. Not a lot of moving parts. Most of the trick to building a rocket motor is doing it to withstand the extreme environmental conditions and to do so while no one is available to service it.
Not being a rocket engineer, I’m trying to figure out what there is to improve to the extent you’re going to call it a new engine, or be distressed when someone will no longer sell you theirs? Improve long term reliability with more modern materials?
The devil is in the details. There is a failure mode so common in rocketry it has it's own acronym: CATO, meaning Catastrophe At Take Off. Basically there is a fine line between blowing up and sitting there uselessly. It's trivial in design to hit that line. In practice though, various parts of the rocket motor must successfully dissipate or scavenge a tremendous amount of energy. Any failure means, usually, lots of heat or lots of vibration (same thing really) gets put into parts not intended to handle it.
Some people think solid fuel motors are really simple because they have no moving parts. This is wrong. The exhaust is moving, the combustion front is moving, the heat is moving, the rocket is moving, everything is moving. Liquid fueled designs attempt to simplify things by precisely controlling what happens in the combustion chamber. Unfortunately for turbopump enthusiasts the engineering of real materials to withstand the forces involved in moving the fuel is a black art. Extending a design tends to require almost as much work as the developing the original one. Incremental improvements thus tend to be cost multipliers, not added cost.
That's why when someone shows up with a design that works in practice, the industry just keeps using it. As is.
I have seen a pump design with far more benign failure modes than pressure fed or turbo pump modes. The downside is you need to expend a major quantity of helium to launch a space-x sized payload.