Couple of notes here, but I'll try to be brief.
Blacksmith points out that an ImmoRush as a deck archetype is extremely versatile in nature, which is what makes them so interesting. However, vNG is a rather specific variation. While there is plenty of room for experimentation, my intent with this deck remains firmly planted on the original foundation: to bring stability to what would otherwise be a hit-or-miss deck reliant on good RNG.
That is the cornerstone that I use when determining whether or not a change I'm considering is in line with the deck as a whole. This is how I arrived at the original variants and even more so the latest one. It is the step I excluded when I posted GoD and vE, which is why I do not like those variations now. I find that GoD relies too heavily on Destroyers and Gemfinders which actually leads to more bad hands than other variants. vE made the mistake of reverting to an Earth Mark, which is not ideal for the sake of stability.
Marks:
When the original variants were posted, decks as a whole were slower and packing less CC than in today's meta. As a result, stability didn't make as much of a difference in the long run as it will now. This is why having a Fire Mark is superior to an Earth Mark. In the extremely short games, the Growth ability won't actually be very important because the game ends fast enough that running out of Earth Quanta is hardly a problem. In the extremely long games (against lots of CC) the Destroyers will most likely be removed permanently and the Earth Quanta piles up uselessly. A Fire Mark helps wean the deck off of RNG in the early game and the extra Fire Quanta will definitely have an impact in longer games (7+ turns) when you consider the extra creature(s) that can be played off of the mark alone.
Quanta:
Even with the Fire Mark I found it is better to avoid too many Gemfinders as fodder because they will inevitably lead to bad drawing if there are too many. Ever since the advent of the Minor Phoenix, four fodder has always been enough. I see no reason to change that now. Balance that with the six towers which have always been the ideal number, it would seem, and you have the buffer needed to rely on the Minor Phoenixes as the catalyst for deck launch. These simple ideals result in a reliance on Fire itself that makes bringing in splashed cards less ideal than in most other variations. The Phoenixes and Seraphim take that place instead.
It is also worth noting that as a result of easing the burdens on Fire Quanta, this deck can and does get by without a weapon. Not requiring Fire was the single greatest benefit to a weapon, along with the fact that it made three turn wins possible. The weapon itself is not fundamental to the core of the deck given the notable changes to quanta balance achieved in recent times.
Ugh. That was a lot longer than I expected, but I wanted to fully explain some of the reasoning behind what I'm using (I'm not quite as whimsical as I usually like to portray).