SGC, as you describe, there might be problems, but even at LHR there could be advantages in using MLS.
One LHR study considered parallel glide paths, conceptually similar to the current long body PAPIs, but spaced well down the runway to avoid wake turbulence. The theory being that the jets requiring shorter field lengths could land long whilst the heavy jets landed normally. The approach sequencing would use methods similar to current procedures, but could use closer spacing not having to maintain the normal wake separation. The advantage of this arrangement was greater if the long-landing aircraft could also fly steep approaches.
Other ideas involved simultaneous off-axis helicopter approached paths enabling full IFR operation, (including Cat 3?).
Also, there were many studies and flight tests involving two stage approaches, mainly for noise benefit.
Noise preferential routings were considered for MCT where standard curved/segmented azimuth tracks would be flown by all aircraft, primarily avoiding hospitals thus meeting the local requirements.
Re approach surfaces, IIRC one MLS manufacturer (Bendix?) developed a 3D math model involving terrain and standard terrain clearance values which optimised routeings for an acceptable glidepath angle. The system may have been used with ‘private’ MLS installations in the USA e.g. Aspen, Vail, (1980s?).