The article talks about several issues, such as:

- Pathfinding when taking up more than one tile

- Area-of-effect (is damage multiplied per tile?)

- Collisions (particularly if the entity is not square/rectangle)

- Visibility

Honestly none of those sounds particularly challenging. The hardest is probably the path finder but even that is just 1 tile patfinder using a corner of your square except now you need to check more squares if you are able to move in a direction. But combined together, those and many other small code & design issues add up and becomes a pain

Imo the reason why roguelikes dont add them is simply because it adds very little value comparable to head aches it can cause

"Honestly none of those sounds particularly challenging"

Individually? Sure. Together? Kinda rough. Interacting with every other system you've ever put into your game and with every other system you ever will? Yeah, it can be challenging.