Switch hitter warlock?

[Noldo]

Since blade pact warlock can shape his signature weapon to take a form of whatever weapon is most practical at the moment, could it be used as basis for a switch-hitter build that would be optimized to vary the fighting style to fit the situation or is the difference between greataxe/greatsword (as 2-hander) and a longsword (as versatile weapon) too limited for such a niche build to function?

One would need to be STR based in order to get value out of 2-handers (where appropriate), get at least 3 levels of warlock (for pact of blade) and most likely some combination of Fighter, Paladin and Ranger in order to pick fighting styles since you would need at least dueling and great weapon fighting to excel in two different fighting styles.

[Joe the Rat]

Duelist / Great Weapon is probably the best combo here, as Two-Weapon would require you to pull another weapon. Though if you really want to up this from "Versatile Plus", you should look at switching Greatsword / Polearm (reach) / Longsword (duelist) / Spear (duelist/thrown) for full effect.

The catch is that changing form takes up an action. You'd need to burn an action surge (from fighter) to change form and attack in the same round.

This would actually work better on an Eldritch Knight - They can have two (at least) bond weapons, and summon those as a bonus action. Longsword attack / drop / bonus action summon halberd / slash / next round.