Why clone 4e? WotC is still printing and selling 4e.
WotC hasn't put out anything substantial for 4e since 2012, so while they might not have sold off their back stock yet, or might even say it's nominally still in print, it's been languishing essentially (pi) nu-supported for 2 years. Long enough to for a lot of pent-up demand for 5e to build up.
To clarify: I'm curious what 4e fans would consider an improvement of 4e.
Not something I've spent a lot of time thinking about, really. Through the edition war, which raged from the moment 4e was announced until it was dead and buried, 4vengers thought more about defending it, and during the 5e playtest, it was more a matter of trying to get some fraction of the good stuff from 4e into 5e, so it might potentially be /almost/ as good as 4e.
While there's a lot you could do to make 4e better, there's been no prospect of D&D continuing in those sorts of directions.
So, while it's fruitless speculation, things that might make 4e better (or make good modules, options or alternate 4e-based games):
- grouping powers under Source instead of class (cuts down on redundant powers, makes Source more meaningful - more racially, you could split Source and Role from class, letting the player pick and choose from among Source & Class powers and Role & Class features.)
- loosening up MCing by removing feat taxes and just letting multi-classed characters swap powers and same-role features at whim (cross-role features might still be an issue).
- more racial and theme 'substitution' powers to go with that.
- more chargen/development options that open up substitution powers.
- controller role support in the form of class features instead of overpowered controller powers (which screw up the options above).
- Advice, guidelines, & examples of good Epic-level stories and adventures.
- Getting skills onto the de-facto +1/level bandwagon to simplify on-the-fly DCs
- An optional simplified, flat +1/level progression to replace magic-item dependence, stat boosts, and feat taxes.
- A massive clean-up of feat traps, feat taxes, and over/under-powered and redundant feats in general
- further development of the potential of skill-challenge type mechanics, linking them directly to the two non-combat pillars in more structured ways, so DMs have tools for exploration and interaction comparable to those they have for encounter design.
- expansion of interaction and exploration utilities and features for all classes, so classes remain balanced & contributing regardless of which pillar a story or campaign emphasizes.
- expansion of martial practices and other ritual-like options for sources that rituals don't fit
and, of course:
- an OGL, with emphasis on the O, so lots of other games could be developed using the 4e-isms like surges, action points, powers, &c that would work /so/ well in such a range of heroic genres besides fantasy.