Rabid_cog, there have been some changes to shields already. They no longer consume fuel, and are now variable in size, with larger shields getting improved shield points per HS.
I like the idea of leaky shields, primarily as it does require them to be combined with armor, and also I would like if both sides in an engagement take some damage, and one side does not come off entirely intact due to shielding. So making it damage mitigation instead of damage prevention helps there.
However I don't see the first levels being not very useful as too big a downside. Some technologies coming in as they advance is quite nice.
Overall you still need to change SP per HS as tech increases to keep up with armor, else it is too powerful or useless at one end of the tech tree or the other.
Further, basing penetration entirely on tech is not desirable, as currently shields are a 'big ship' toy. They get linear scaling in shield thickness, compared to x^2/3 of armor thickness. They should still get an advantage of mounting large, heavy shielding compared to tiny ships mounting just a single shield. However if you instead had a penetration depth of SQRT(SP/5), where SP are the max number of SP on the ship (only working shield generators) you would get a shield that does again require a significant hull to be effective.