As many as most GPUs without all the extra cost and power draw. Nvidia sets a transcode limit of 2 sessions unless you disable it. You really shouldn’t ever be transcoding 4k content. Most people will duplicate 1080p and 4k content and not share the 4k library for remote streaming/external users to avoid transcoding, and 1080p transcodes are no sweat. Furthermore, the goal should be to avoid transcoding wherever possible, so it’s unlikely that you’d have multiple people doing intensive transcoding simultaneously if you follow the above advice. You’ll want everyone to direct play as much as possible.