4-6 is a part in some playbooks and I see no reason why you shouldn't be able to use it especially on early downs. Some playbooks have very nice blitzes from 4-6 and still most relevant types of zone defense.
If you want to defend 3 WR sets with a 4-6 you may need some faster LB or put a S in there, otherwise it might be tough. But still if you have a fast, agile LB with 85+ speed, you can defend most WR's. Just don't put them 1 on 1 with Tyreek Hill on a deep pass
PS: I will try this year to have 4-6 as my base defense in CFM. Will see how it works