Hi Steezy,
I've not ridden an Equilibrium but like you I'm a big fan of the look of a steel bike. I have tried searching for a review of the 2015 Equlibrium Disc 10 to read someone else's opinion but I can't find one. Therefore I'll be really interested if anyone with one posts a reply.
Re: the frame the only thing I've been able to find following a quick search about the Mjölnir is taken from the Genesis catalogue, link below, but if the link to a pdf of their catalogue doesn't work I've copied the text.
http://www.genesisbikes.co.uk/img/uploads/files/genesis_cat2015_web.pdf
"Mjölnir
AKA ‘Thor’s Hammer’ and pronounced
‘Myol-n(ee)r‘ our new double-butted, cold-drawn, seamless, Taiwanese chromoly tubeset also goes by the aliases of 4130, Cr-Mo and Chromo. It’s a like-for-like replacement of Reynolds 520 tubing which helps keep a lid on price without sacrificing performance. And herein lies the reason for the switch – a saving can be passed onto the consumer via either a healthy price drop or a little more room for up-speccing. We think the switch makes total sense; same weight, same great ride characteristics but a heck of a lot more bang- for-your-buck, no-brainer."
The Day One Alfine 8 had the Reynolds 520 tubing and Genesis say this is a like-for-like replacement but this isn't an independent opinion so I guess you have to take their word for it. You could get a better steel frame but unfortunately as with everything it'll cost more. I don't know if you've got any LBS anywhere near you that sell Genesis bikes but if you do have something nearby and can get to it it would be worth going to have a look especially if they have Equlibrium models in stock so you can see what you think of them in the flesh.
Re: the Alfine 8 and the 520 tubing I appreciate that it wasn't the lightest bike in the world compared to todays standards. However for me I'm not racing anyone on my ride to work and a comfortable, reliable bike that will work in all conditions and fingers crossed last a while was more important to me than going down the route of the lightest quickest bike that I could find. One thing to say though is that despite riding for a long time I've never had many bikes and I've not owned any light weight racing bikes. Therefore to me I had no problems at all with the weight of a hub geared, Reynolds 520 steel bike but for someone else if they'd been used to light weight carbon racing bikes they might well feel a different way.
I'm still saving my pennies towards my next bike and I'll be interested to hear what you go for whatever it is. Also if you manage to get a test ride on an Equlibrium I'd also like to hear back on what you think.
John