I am not al lthe way there yet. In part because I see real issues with responder no longer being entitled to expect xx at a minimum in terms of support. While I appreciate that the 4th suit sequence 1♦ 1♠ 2♣ 2♥ 3♥ is a problem so is the idea that responder with AKQxxx in ♠s cannot count on a 68.5% or better chance of no losers and 6 winners! And that is only one example of many issues that arise when opener can be 1=4=4=4 for 1N.
Another, and more prosaic issue, relates to when responder should pass 1N with a 5 card ♠ suit and a weak hand.
My almost invariable rule, opposite a 1N opening bid, is to get to the major. I only depart from that on hands such as 9xxxx Q10x Qx Kxx.. where all my stuff is in the short suits...
Admittedly, one of the upsides to that approach is that once in a while we get to a 9 card fit, which is no longer an issue in the given auction.
But I still like to bid 2♠ on most 5332 hands after a 1N rebid, and experience suggests that this style is a consistent, altho not an assured, winner. In part because the long ♠s will usually score tricks while controlling side suits at a suit contract and be unusable in notrump and in part because of the preemptive effect.. compared to 1N being passed to 4th chair may be able to compete (opener is not USUALLY 1=4=4=4 even when that style is permissible).
If we rebid 1N on 1=4=4=4 hands, we will play 1N with 18-22 hcp and a 5-3 ♠ fit with, say, a combined ♥ holding of xx opposite Qx on occasion.... or play a 5-1 Qxxxx opposite x ♠ contract, with 4+ trump losers, when 1N was on ice.
For me, this is a work in progress: I have to convince my partners to experiment and, at our age, our urge to experiment has diminished

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