They are actually quite effective but you have to remember that the nova knives are not the sort of weapon to be used by rookies. They are weapons for professionals only who know how to properly use them. This means that the nova knives present the ultimate challenge for the extremely hardcore players who strive for a challenge.

For these dedicated people are the knives really an equivalent alternative to other sidearms? Or is the extra challenge more of a gimmick?

I am by no means a badass with nova knives (I think you've actually shot me in the face while I tested whether frontal assault was viable) but I've found that they have a role in which they're better than other weapons. All of the times I've died with a knife ninja build (knife as primary, 2x sidearm modifer, 2x kinetic catalyser) have been experimenting with taking that build outside of the role I find it excels in.

Even though sprinting with nova knives isn't properly implemented yet (though I understand it's coming SOONGäó) it's still possible to do and, for me, that's what makes them unique. I've had a lot of success with sprinting hit and runs, being caught in front of a heavy and exploiting their slow turning to get behind them and strike. I don't think I would have had the same result if I was running a shotgun scout (which is admittedly better in many situations, like narrow hallways).

When I've stuck to sprinting between cover and flanking with knives charged, I've had more success than doing the same with a shotgun because I can make the attack part of my sprinting past and back into cover.

I was surprised after searching the words "nova knives ignore shields" and getting no results. It seems like a natural idea for making them worthwhile. Not that it's necessarily a good idea, but I am surprised it hasn't been raised. What do people think? OP? Tacky? Worth exploring?

I find that success with most weapons is based on the idea of playing to that weapon's strengths (obvious I know but anyone on the forums has seen their fair share of people complaining about exactly this). If it turns out that the forthcoming sprinting nova knives work then problem solved. I just thought that given the general consensus about their relative strength it might be useful to discuss more interesting changes than a simple damage buff.

I think there should be racial variants for melee weapons. They'd all work off the same skill, but be functionally marginally different.

The current nova knives look Caldari in design. They deal a lot of damage, but take two consecutive swings to use.
A Gallentean design would be perhaps more look like a set of small kris. They'd deal slightly less damage, but be quick to charge and strike both hands at once.
An Amarr variant could be a single large dagger that takes longer to charge but deals massive damage in one strike.
The Minmatar could perhaps wield a sort of Nova Axe that looks like a Sci-Fi Tomahawk.