As near as I can tell, the implementation of it would be largely situational, likely as a compliment to unpowered body armour or as an example of low profile armour. I mean, there are plenty of situations where where you would want protection but for various reasons wearing power armour would be impractical. Like has been pointed out, it'd be excellent for VIPs or police where the cost factor and/or intimidation factor of full power armour is undesirable. So they're not so much PA replacements, since a suit of power armour offers much more than just the ability to mount a shield (power assist, heavy armour for when the shield fails, enhanced mobility, greater weapon options, etc). They might be useful for light infantry, depending on what the system would cost relative to a suit of power armour, but for the most part they'd see use for non battlefield roles. MPs in the military, civilian police forces, perhaps garrison troops, that would be the use for it.
It's just like how despite the fact that we can develop armour that can stop armour piercing rounds (class IV body armour), there's still an extensive market for armour that can only stop smaller rounds. So the PA still rule supreme over the battlefield for their mix of survivability, manoeuvrability and firepower. But personal shields would allow for conventional foot infantry to survive at least a little while on the battlefield. They wouldn't be a mainstay by any means, but it would allow more tactical options, either from the perspective of allowing you to field troops in desperation without it being straight up suicide or simply being able to field more troops with less training (takes less time to train someone to turn on a shield and hug cover than to pilot a PA after all) and potentially less cost.
And I should add, given the issues of bulk and the like I don't expect personal shields to be nearly as effective as what's mounted on even the lightest of PAs. I'd expect 5 points of protection to be about the max that could be made, at least initially. I don't really see it changing the feel of the setting very much. It's not like Hanako is going to get into a punch up with a Ripper in her evening dress and be able to survive just because she has a shield belt on. It just offers a few more avenues for GMs and players.
Just my $0.02 as I try and move to posting in more than just a handful of forums here.