Was taking a break from work and decided to do a bit of googling regarding the new law in Thai and found a couple of interesting articles, all published by Thairath in the last week or two.
Seems that there is still a lot of confusion and contradictory articles out there. One of them was an article about Chinese tourism in the north, which completely avoided the new rules that WILL go into effect claiming that by the end of this year there could be 25,000 Chinese registered vehicles entering Thailand for tourism, after the 12,000 that came so far in the first 4 months of this year.
This is highly unlikely, given all the new requirements, particularly the one that will limit travel to the border province entered, except for special cases requested at least 30 business days in advance. The reason why so many Chinese vehicles came in the past was because entry was easy and almost free. This is about to change so even though they can still come, to suggest the numbers will be as high as claimed is ludicrous. They will go down, because the idea is that the authorities and local residents don't want to put up with large numbers of holidaying Chinese causing accidents on the roads and causing congestion hence a major reason why this law is coming into effect.
If I were to make a guess there will probably only be 1000-2000 more Chinese vehicles entering by the end of the year, the vast majority will be coming on rally type tours since they won't be allowed to enter without making pre-arrangements anymore.
This is also the basis of a last-minute meeting conveyed by Thai based tour operators in the north, who want to see the following changes made to the law by the Land Transport Department (I am translating from the Thai language article with link at the bottom of this post):
1. They would like the new rules to be delayed in order to allow for opinions on the law to be made by concerned parties (I thought this process had already occurred - seems to me that these tour operators are only concerned with their own interests - where were they back in February/March when this new law was debated?)
2. They want the new rules to only allow vehicles with no more than 7 seats including the driver to be allowed entry, not 9 as per the current ruling in order to prevent private tours. This is a bit of an odd one.
3. Vehicles brought in by tourists should be allowed to drive outside the border province entered due to having purchased insurance and being under the control of the tour operators already.
4. Vehicles brought in should be allowed to travel to other provinces in order to exit for other countries. (Seems that these tour operators appear to have little knowledge of the fact that entry into these countries is at the discretion of local authorities. Myanmar doesn't allow entry without a tour with arrangements made at least 30 days in advance; Cambodia generally won't allow entry either except at certain crossings with special conditions, while Laos will allow re-entry at any border crossing. For Malaysia I'm not sure about the requirements to enter if you're driving a non-Thai vehicle, but again, that's at the discretion of the Malaysian authorities. Therefore, it should be assumed that Chinese tourists are coming just to travel to Thailand and not other countries).
5. Permission to allow travel across provincial boundaries and other conditions should be allowed to be requested 10 days in advance (as for the basic permission) not 30 days advance notice. This relates back to points 3 & 4, since applications made at least 30 days in advance allow this.
While there may be some tweaks to the rules, given it's been made law, this last minute "cry wolf" attempt by these Chiang Mai and Chiang Rai tour operators is unlikely to have any immediate impact since the rules will go into force on Monday (27th June).
Since it's a new law, no, it shouldn't be delayed. However, streamlining the rules that will allow applications for all cases to be made 10 days before and allow travel outside the border province entered is a good idea.
It could be however that the Land Transport Department will only allow registered tour operators with multiple vehicles travelling on rallies to be granted these special conditions, with other vehicles entering independently subject to the rules as outlined in the Royal Gazette.
It looks like we will know more once the rules do go into effect next week.
Nothing about motorcycles or motorhomes, but I suspect the "special case" ruling will apply - meaning you will be allowed to bring these vehicle types in but with 30 days advance notice.
For anyone that reads Thai (or has someone who can translate) here's the article I was referring to:
http://www.thairath.co.th/content/645692