Current state of AT&T bootloader? topic

My partner is looking at getting a new phone, and we are looking around at different models. We want one that we will be able to upgrade and flash custom ROMs on for obvious reasons. For the AT&T model, what's the status of the bootloader? I have read that someone had an unlock method a few months ago, but I've also read that new models have an update that breaks that method. Also I have read that there is a safestrap method to install custom ROMs without having to unlock the bootloader.

Can someone summarize the status of the above for me? We would be buying a new one from AT&T. Would we be able to unlock the bootloader, or use safestrap?

Thanks!