I have what is now a tired iPhone 6s. There was no way I was going to pay circa £1K for a new iPhone but the £419-£469 for an iPhoneSE is far more realistic. So I would certainly agree with the sentiment that SE sales are going to be bigger than expected.
I would say however based on long experience with Apple that this will have a smaller detrimental impact on sales of high end models than other brands would see in the same situation. That is people who would go for the new top-end model will continue to do so, people (like myself) who have held off upgrading for a long time due to the obscene cost will now feel able to do so.
Logically it should also have be a big help in developing markets like India.