Really need a challenge, playing on survival and can headshot kill anything with my sneak attack x 5.3, gauss rifle sniper build!

There should be more BIG bosses like the huge mirelurk at the castle, do you think there will be a mod for this?

Yes.

You could also try not cheesing everything with suppressed headshots.

Throw on some power armor and a rolling pin and get to work

there will absolutely be mods tweaking the difficulty of enemies. Im sure there will be a ton of variety for different types of difficulty, such as a mod that makes enemies take more damage, or a mod that makes every thing more powerful so that gun fights are determined by one or two shots (eliminating situations where enemies or yourself from being able to take 10 shots to the head.)

Take most OP perk and weapon = game is easy

It's not an mmo. You are the arbiter of your own challenge and enjoyment.

Use sneak with melee primarily and it's a lot more enjoyable. However sneak has been OP in every game in this engine. If you don't enjoy it you should have not opted for that play style.

I think there will be mean monsters from mods in the future. For me it's fine as it is, I don't like boss fights. I was nearly about turning difficulty down in the Mirelurk Queen fight.