I posted this on another thread. Game engines are always a work-in-progress. I used an analogy of a car. You can spend millions of dollars and many years re-inventing the car but when all is said in done it will look almost exactly the same as it did before.
Or, you can strip a current vehicle down, replace new parts and add some to increase performance, add a new interior complete with new seats, dash, and electronics, give it a new paint job, and spend half as much money and time but still have an equally performing car.
Your choice