BIP 148 (aka UASF) is not accepted by pretty much all developers. It has not been accepted by Core nor is it likely to be accepted and implemented by Core. As of now, the segwit implementation in Core is as is specified in the segwit BIPs, which do not include BIP 148.
I'm waiting for an implementation. Once we have a reviewed and tested implementation, I will upgrade my node to activate UASF at whatever date has most support from the community. Miners had a lot of time to upgrade. Alts are advancing. I'd prefer to activate UASF sooner rather than later.