What have the recent changes been to Thai visa rules for long stays, especially for those crossing from Vientiane?

Bottom line, you probably won't get a visa, either in Hanoi or Vientiane. But may as well try. You will not likely face any issues or questioning coming back by land visa exempt, just need to bear in mind the hard 2 per calendar year rule. Coming back by air having spent a lot of time here is much higher risk, whether you have a visa or not, particularly to Bangkok airports (and if you say fly from Vientiane is that to a Bangkok airport as they don't fly direct to CNX). CNX is lower risk but still higher than the land borders, which with Laos and Myanmar are still no problem.

You can plan what ever you want, problem is that Immigration does not care your plans. They want you to follow the Thai law. You have a longer history of spending time in Thailand, it will be more and more difficult to get a Tourist Visa at any Thai Consulate in the this region. Going in and out Thailand with the Visa Exempt Entry and Extensions of Stay is possible and allowed to a limit of 2 a calendar year by land borders and no limit by air. To many people using the short time possible visits like the Visa Exempt Entry, the Tourist Visa and the Non Immigrant ED visa to live long time in Thailand and that is not why these options are available. BUT what is contradicting in advice, or what people do forget: YOU do not have any right to enter Thailand, even with a visa in your passport. YOU ask permission to entry this country at an Immigration check point where an Immigratio Officer HAS the right to say NO.

Rules have changed, in particular at Vientiane and other consulates. Vientiane is now refusing tourist visas if you have been in Thailand six months. If you are going to Hanoi anyway, try for the visa there first. You can try again in Vientiane but you'll probably be denied.

You'd be better off entering Thailand by land from Vientiane then at that point rather than flying. You can fly back from Udon Thani. With border bounces and extensions that will bring you up 120 days from Jan 10 which is start May. You'll probably be a few days short of your return May 15 so next bounce maybe plan to spend two weeks somewhere else like Laos before you come back.

This is considering you have already booked this travel to Vietnam, Siem Reap, Vientiane. This isn't optimal for getting to May 15 in Thailand but if it's what you want to do.

Rules did not change since 31 Dec 2016, not sure when you made your planning to visit Thailand for 9 months and why you do not want to buy a visa which makes a longer stay possible. Get a visa or face extra questions on entry, be prepared with the minimum 20.000 Thb cash, proof of accommodation and onward travel. Have a plan B just in case an Immigration Officer does not believe you are here on holiday.

If you do a land border run Dec 1 that can bring you up to end January with extension. Your land visa exempt entries reset Jan 1 so you can do two more of those in 2020 which with extensions = 4 months bringing you to end May.

You can mix in air entries and going to Vietnam if you like, although these are higher risk. This is just how you could maximise with land visa exempts and without getting a visa.

No, but here is what *may* work.

1. Fly into Thailand on a visa exemption on Jan 10. It'll give you 30 days.you can stay until Feb 10 ( or thereabouts)

2. Extend that visa by 30 days. That'll give you until March 10 (or thereabouts).

3. Border bounce. It'll give you another 30 days, so until April 10, or thereabouts.

I doubt that you will be able to obtain a Tourist Visa at Vientiane. Certainly not at Savannakhet. And likely to be denied a Tourist Visa in any SE Asian Thai Consulates. Times are changing. Good Luck.