No, most certainly there won’t be trains by default on MSFS 2024. I have assumed that for two reasons:
1 - they didn’t mention anything about train traffic. They specifically mentioned improvements for road traffic, sea traffic and air traffic. I believe there’s no data provider for worldwide train traffic.
2 - What I mentioned on the posts above. In their wishlist chart, train traffic is tagged as not planned. All features coming to 2024 are tagged accordingly.
And about the train traffic add-on, there’s one recently released. If you want to know more about it, see the topic below: