LOL I asked that question to myself a couple of times. Definitely regretted buying the play model as the play part was essentially useless for me. If Synology again, I'd go for something which is docker compatible (some recent + model). With that you get lots and lots of additional possibilities, but since I have never tried to realize 1080p h264 on the fly transcoding with such a setup, I cannot really recommend this to you either. My next NAS will most likely be self-built and run Ubuntu server to avoid these kind of problems in the future, but again, not enough knowledge / experience to give you some specific recommendations hardware-wise. For the time being, I simply don't transcode, which actually works pretty well for me, too. I have hard-wired Intel NUCs and RPi2s and some wireless tablets as clients. Only bottleneck are the tablets due to their WiFi connections, but that still allows streaming SD channels, so I have configured TVH and tags in a way that I can acccess either all channels or SD channels only, depending on the device.
Not very helpful I suppose. But I'm sure there a people on these forums (or on #hts) who can give you better recommendations on transcoding...