On the topic of fixing, I think the BFZ cycle of lands is severely underrated in how well they supplement an environment where you're looking to push the goals highlighted above.
In the earliest iterations of my cube the mana fixing was double shock, double fetch, and a mostly manland 5th cycle. Problems arose in that with a higher power level and modern designs giving you more bang for your buck, having great fixing usually meant that you could cover most of your weaknesses with a variety of effects and payoffs and stabilize in the mid-game. Once your mana base was established, even if you hurt yourself with a few shocks to get there, you could usually just stabilize with a few value midrange plays and get right back on track.
Once these came out in BFZ I made the swap where I could and they were EXACTLY what I was looking. I didn't want to wholly neuter players from branching out for 3+ color decks, but I didn't want it to be as easy for savvy players who learned from draft formats like KTK where prioritizing fixing meant that you could take a small hit if you could recoup that with chaining value as the game developed. These lands rewarded fewer color decks, made sequencing matter more for decks that wanted to curve out, and provided the necessary downside of entering tapped for decks that wanted to get extra greedy. I'm still running a 2nd set of shocks for enemy pairs for now, but as soon as these are officially printed I'll be completing the cycle and will consider my mana base complete for the long haul. They're that good if you still want to have a higher powered environment with fetches and like but are looking to disincentivize extremely greedy piles as a go-to option.
For gold cards I think you need a handful of generically good cards here and there because not all drafters will be as savvy when it comes to exploring and identifying archetypes during the draft process, but a big key is having enough of those specific signposts/payoffs that cause players to re-evaluate other options in that pair. I'm a big fan of
Ob Nixilis, the Adversary because it's rather lackluster in unfocused decks, but can be a real workhorse in something like a B/R Aggro deck with aggressive creatures and recursive bodies. A card like
General Kudro of Drannith synergizes great with the cheap humans in a B/W Aggro deck and can push a
Champion of the Parish or
Bloodsoaked Champion to that critical 3 or 4 power to really force some tough decisions.
And if we go into non-gold inclusions we get cards like
Urza, Lord High Artificer and
The Antiquities War that are lackluster in generic builds, but they become strong curve toppers in a U/R Artifacts shell. If I see a
Rofellos, Llanowar Emissary I anticipate that aside from being the king of dorks that a G/x super-ramp deck is viable and I should be playing a lot of forests and fewer other colors.
Felidar Retreat looks cute on first glance, but combine that with offerings like
Kodama of the West Tree and
Knight of the Reliquary and you can begin to see the shapings of a GW midrange deck with some cool interactions.
Tireless Tracker needs no additional help to be an All-Star, but throw it into that mix and you can push it to Superstar status.
It's all about presenting players with that density via thoughtful card choices and allowing them to peel back the layers of individual cards and discover those interactions and synergies. In all the years I've been on these forums I'd say that that's the biggest thing in common between the designs we have around here even if they vary in terms of raw power.
What I like about seeding like I suggested is that you guarantee every color is evenly supported. If you see only fixing in the wrong colors, that's a good sign then that your lane isn't as open as you thought it was.
