What would Luke Jackson need to average to be a workable F6 by years end?
It really depends on what you project for the forward group.
I personally think F6 line will be in the 100+ range this year, there are a half dozen young guys all with positive fantasy moves and a few proven 100+ senior guys in the current group and when you add a couple of DPP changes I think you will see 6+ guys in that range. Jackson at 72 probably needs to get within ~6-8 of that before the lost points will start to eat the value pick.
So if you see F6 at 100, I'd say you're looking at around 93 for Jackson and you'd be able to hold him for the season. Move that up or down with your projection line. If he plays 22, given this forward group's collective durability, that would also go a long way.
It is worth noting however that the makeup of the premium group above the F6 can be very important, if F6 s 100 but F1-5 are all 110 for example, then you can only afford to really have one guy using up your F6 spot and basically need the other 5, this is an extreme and unlikely example, but it scales back with 1,2 or 3 guys in that range still.
There is also a final bit of value with a DPP R where they can gain on their effective average if they help you avoid donuts that other's can't. So say everyone has Gawn and he misses a week, you have Jackson to cover and get whatever rookie forward score you have, while others are forced to either trade or cop a donut, you can realistically include that rookie score in Jackson's total. Obviously it's not ideal as not everyone is likely to have the missing ruck, but it's still an effective gain.
That said, I don't really like Jackson to score 95+ as I don't see a huge role change for him or that much natural development, in fact there's a case that the more ruck time he gets the more time he'll be rucking against the opposition #1 where he is generally the inferior ruckman instead of getting to feast on 2nd rucks where he's generally the superior ruckman. Terrific talent but feels a year or two early to me.