Fully separate DFAs and NFAs (or use a "sliding scale" representation)

[jn1z]

Originally everything was represented as an NFA, which is very costly for peak memory and is difficult to maintain.
This was addressed to a large extent in Walnut 6 and Walnut 7 changes up to now, but there are still many issues with this.

Alternatively, there could be a "sliding scale" representation, that represents some states as DFA and some as NFA. Either works.

[dvberkel]

A cleaner separation between different classes of automata would be beneficial

[shallit43]

Yes, it would be nice (for example) to have an option to return an NFA if the last quantifier was E (there exists).