I don't believe there is a practical limit to brightness as long as the beam is shaped and aimed properly.

Motor vehicle headlights drown out my bike lights as they approach from the rear. 1850 lumens on my bike is inconsequential compared to the thousands of lumens put out by modern automotive systems as a car passes.

It is certainly possible to buy a bicycle lighting system which overpowers automotive headlamps but this thread asked about practicality, not possiblity. Most would not consider such a system practical from either a cost or form factor standpoint.

Running 2000 lumens would be possible for under $250 - two Light & Motion Urban 1000 lights, one on the bar and another on the helmet. This is probably close to what many would consider the practical limit and the vast majority of automotive systems are much brighter. Certainly the OP's 700 lumen light is nowhere near the practical limit.

-Tim-