Backporting Starfinder "Double Attack" into Pathfinder?

[Machinekng]

So, as part of one of the Starfinder teasers on the Paizo blog, it was announced that one of the key mechanical differences between the two games would be that the full/iterative attack system would be replaced by having the ability to "double attack," taking two attacks as a standard action with a -4 to hit. It was also revealed that abilities that would normally grant an additional attack in 3.P (i.e. haste) would be changed to reduce the hit penalty for using a "double attack".

Now, with the issues that iterative attacking has in 3.P (limiting mobility, making pounce almost nesecary, 5ft. shuffle, etc.) the ability to be more flexible in combat is interesting. While it'll be a few months before the system can be seen in the context of Starfinder, and how well the revised mechanics mesh, I was wondering how adding the "double attack" as a houserule in Pathfinder would affect gameplay. This would be as an additional option, alongside full attacking. Feats like Rapid Shot, Two-Weapon Fighting, and others could have addendums to provide support for the new feature. Rapid Shot would simply reduce the penalty when double attacking at range, and Two Weapon Fighting would have an additional ability to reduce the penalty when using two different weapons to make the attacks.

Now, my questions are:

1.) Would this new feature be too optimal, in that it would always be better than a single attack or full attack, unoptimal, in that it wouldn't provide much benefit, or somewhere in between?

2.) What issues would there be in adapting feats/items/class features to the new rule? Would there be any intractable problems that would arise from the interactions? Would it lead to any class balance problems?

3.) Would it actually improve the playability of "mobile martial" characters?

[stanprollyright]

Star Wars Saga Edition has a similar mechanic, where Double Attack and Triple Attack are feats that impose a -5 penalty. It was a bit wonky in that game because defenses scaled faster than attacks, so high level characters invariably took those feats and then spent a bunch of their talents reducing the penalties.

I also played in a 3.5 game with a house rule where if you didn't move you could get two standard actions a round. The problem was, we were like "what's the point of TWF, Flurry of Blows, etc.?" so it ended up in effect becoming 2 full attacks a round. It gave a huge advantage to the "oversized twf" guy (though casting twice a round was pretty cool too).

Now, to your questions:
1) it seems like once you have a feat or two mitigating the penalty you would pretty much always want to be using it. So the first one, I guess.

2) Some classes benefit a lot more than others from getting multiple attacks (looking at you, Rogue). So there would be some balance issues. It also undermines one of the big advantages of full-BAB classes, namely iterative attacks. Other issues: what happens if you combine TWF and Rapid Shot? No penalty? Another attack? Is there a melee equivalent to Rapid Shot that doesn't involve two weapons (Rapid Strike)? How does the change affect natural weapons? Are there ANY benefits to standing still and attacking?

3) It seems like it would benefit skirmishers a lot, but on reflection it just turns everyone into one. So the net benefit probably goes to the big zweihanders who don't lose anything and gain double damage and extra mobility.

[Sayt]

It feels a bit early, as we don't have some details yet. For instance, I thought it was a full round action.