Everything is at the discretion of the immigration officer, but if you do not have any recent prior entry history, my understanding of the new guidelines is that you may enter and obtain a total of 90 days — that is, a 60-day visa exemption with a 30-day extension, as before — and then make a border crossing by land or air to receive a new 60-day visa exemption. However, you can only obtain a seven-day extension on the second exemption if you arrive by air.
You are not planning to do a visa run to a nearby embassy to obtain a new visa; you want to make a border crossing and receive a new 60-day visa exemption. If you do not have any recent or extensive entry history beyond your current entry, you should be able to do so. If you cross by land, you should expect to spend at least one night outside Thailand. You can only receive a 7-day extension on your next visa-exempt entry if you arrive by air. In any case, you should be prepared to present an onward ticket within 60 days.
Extensions are also covered, but border bounces are being targeted just as before. This has now been formalised as a maximum of two in a row without returning to your home country.
The embassy in London is known for being one of the fastest, with many applicants receiving their visas within just a few days. The formal processing time is 10 working days. I am aware that it has taken longer recently, and several applicants have been informed to expect a processing time of around 15 days.
There is no communication between the embassies that issue visas—where you provide a travel plan—and Immigration regarding your actual entries. The TDAC is merely an electronic arrival card, and providing an intended departure date is optional. When you are stamped in on a 90-day Non O visa, the day you enter counts as day one and the day you leave counts as day ninety.
With a one-year Non O-A visa with multiple entries, you may, under certain conditions, stay in Thailand for up to two years before applying for a new visa.
If you are planning a longer-term stay in Thailand, the most practical option is to apply for a standard 90-day Non O visa before travelling and then obtain annual extensions of stay at Immigration in Thailand.
You cannot convert your visa into anything else, but you can apply for a new visa at the embassy in your home country or apply for a temporary stay permit -Extension of Stay- at Immigration in Thailand.
The summary regarding visas is clearly correct. As for the interpretation of the new visa-exemption guidelines, what has been written is consistent with the information currently available from the official police order. We all need to observe how this is applied in practice over time before we can state with certainty how it will ultimately be implemented.