At this point 1500 is the standard, we can’t ever hope to increase it without a way to negotiate the acceptable value across the entire transmission path - that’s what IPv6 gives us.
I'm not sure that negotiating the acceptable value across the entire transmission path is a reasonable thing to do. I'm not sure that IPv6 _should_ be aware of a minimum/maximum MTU of underlying transmission path particularly since that path can often change transparently and each segment is subject to different requirements.
At this point 1500 is the standard, we can’t ever hope to increase it without a way to negotiate the acceptable value across the entire transmission path - that’s what IPv6 gives us.