As someone who worked on PLC at university:
Yes, PLC is being used for grid control and metering applications.
So, there's already a lot of meters that implement that. There's standards (e.g. EN 50065); you don't seem to have come very far in your research!
Are there any technical/practical challenges to implement a PLC based smart metering network?
Yes. Plenty. Like, really many. Compared to your usual wireless channel, or your usual dedicated communication line channel; even compared to your DSL channel.
For example: Power lines have extremely low sink impedance. That's not cool if you need to generate a signal of significant amplitude.
Then: Power lines have high attenuation. In fact, the higher you go (and I'm talking about a couple 100 kHz), the uglier it gets. But, hope not: Noise is exactly strongest where attenuation is lowest¹. So, worst case for a frequency-selective communication channel.
Then: Many channels are considered stationary; PLC is not. It's very very strongly cyclostationary, with periods where it's nearly unusable. Great!
Oh, and also: where wireless communications engineers often either consider white noise, or narrowband interferers, the usual PLC channel model has several narrowband interferers (often with cyclostationary behaviour themselves), and plenty periodic and aperiodic impulse noise. Impulses are broadband.
Then there's the whole business of not being allowed to interfere with the devices attached to the grid.
Also, but I don't know if this is actually backed by facts, but it does sound likely: PLC, when used in far-reach communications over high-voltage lines, is being blamed by amateur radio enthusiasts for heavy interference. Just another thing that you need to worry about.
That all being said: PLC is dead for indoor internet, exactly for the reasons Bimpelrekkie cites. WiFi is faster (much more bandwidth, even with all the ISM band interference!), also doesn't reach all rooms in a complex building, but is more easily extended, uses less power and most importantly is way way cheaper. PLC seems relatively alive in the grid sector, where having an extra comms line can be expensive. Different countries and suppliers use PLC as their standard for meters, and for smart grid applications. There's been recent efforts to emulate channels² for the sake of being able to actually fully test bidirectional modems with reproducible scenarios (something inherently hard to do, compared to wireless channel measurements).
Generally, the PLC backhaul channel is an interesting beast, and applying what we wireless communications engineers do with software defined radio and cognitive radio approaches sounds wise; if you're into that, look for the dissertations of Kaiser and Otterbach (as soon as they're published).
¹ Han, Kaiser, Otterbach, Stoica: "Noise Characterization and Emulation
for Low-Voltage Power Line Channels
between 150 kHz and 10 MHz", available online
² Han: https://www.ksp.kit.edu/9783731506546