I don't understand why there is a problem here?
Quite simple from a player's pov. If I know posts are set back from the tryline with a space in front in which to score I am far more likely to try and score in that area. I could be diving and sliding on an angle to the posts and then hitting them. Defending players with eyes on getting between me and the ground also have to contend with posts in the ingoal. What about a kick through in goal with the ball in front of the posts? Players will dive at that every day putting a try above personal risk.
How is this different to the present? You very rarely see a player sliding in the direction of the posts at present because of the likelihood that the posts may stop them from scoring.
Basically, opening up an area of in goal in front of a solid object has to increase risk.
Different in what way from scoring wider out?
Think about it. At present when a player is attempting a try while clearly in the in goal you have grounding to judge. Put a post with padding in there an you add another element in goal. Does the 'base of the post/ padding' rule apply from all directions? Has a player touched the post first then slid down it with another player's hand underneath? You are just creating a whole new set of things to look at. I can also see tactics of kicking a ball toward the padding on purpose to create a loose ball opportunity and random luck.
Scrum and maul safety. You don't want players getting driven back into the posts.
How often does this happen? Case history suggests this is not an issue. Why swap one known risk that appears to be very low with an unknown one (as described above) that is unknown as to it's regularity.
(This won't solve the problem with incorrect decisions, and isn't intended to. But it is a lot easier to solve!)
I don't see that it is easy to solve because of the newly created issues that have to be worked on. I'd rather see that effort put into clarifying and cleaning up the breakdown area to make it easier for both players and referees.