I'm still on Fixed outgoing until end of August, I think I was probably one of the last to be able to get it. However, as it currently stands, the Variable outgoing is still 15p/kWh anyway, so nothing to stress about, yet.
I think if Octopus were going to drop the rate this year, they'd have done it at the start of April, so you're probably good until next spring, especially when you consider EON are paying 16.5p/kWh fixed for 12 months.
That being said, I think it's been known for a while that export rates are more generous than is sustainable. You only need to look at what's happened to Flux over the last 12 months.
Also, GaryDoesSolar on YT makes a lot of valid points about where export payments are likely to go, as the grid becomes greener.
One thing that no one has mentioned, afaik, is what happens to export tariffs if/when we move to zonal pricing for import.🤔