I've thought about this for only like 10 seconds so forgive me if anything isn't feasible or sensible.
- get coverage on major free-to-air channels, even if this means selling the coverage stupidly cheap, nobody cares when it's buried on pay tv or obscure if free channels. This is how they completely killed the public interest in the sport over time.
- get rid of the power stage and broadcast 2 or 3 live stages at the START of the rally instead, like 2nd stage and 5th stage or something. Broadcasting the very last stage is dumb because by then the rally is almost always over, it's the nature of the thing. As a kid growing up watching the Rally Vinho da Madeira (local European Rally Championship event) it was always so exciting to wake up early the 1st day and watch the 2nd/3rd stages live as you were starting to learn who was quick and who wasn't, and the crazy-quick but crash-happy guys still hadn't crashed yet. The following day things almost always had settled and whilst there was still a stage or two on the TV, it was less exciting.
- more tarmac events. it should be something like 40% gravel 40% tarmac 20% snow. not 80% gravel 10% tarmac 10% snow as it is now. This made the championship all about gravel drivers, and thrown away the excitement of the randomness of results caused by drivers being specialists in one surface or the other.
- bring back the 1980s style of F1 points scoring, of dropping your worst X scores. Again this would favour the crash-happy crazy-quick specialists, instead of people that are boring but reasonably reliable in all surfaces. And maybe introduce more unreliability, it's so boring that you KNOW cars are almost guaranteed to last the whole event.
- maybe even be more aggressive with tyres, like F1 and circuit racing does. Limited sets of compounds, compounds that are too soft, that sort of thing. Make people work for their tyre strategy to introduce randomness in results.
- more night stages. They shouldn't necessarily be aired live as you can't see ****, but they make for spectacular onboard footage.
- cars that are more aggressive. No idea on how to achieve this, but maybe more power, more weight (to keep speeds in check). I don't mind hatchbacks, I mind boring hatchbacks. Remember the Peugeot 106s and 206s, they were cool as hell. Modern Hyundais are awful.
- MORE cars. I know we have 4 manufacturers now, so that's okay, but maybe mandate that to score for constructors you need to sell cars to privateers for decent fixed prices. And introduce a budget cap so that VW can't outspend everyone else to death. Worst case scenario I'm going to suggest something that's almost heresy and I completely hate in principle, but could keep competition close: a small amount of extra ballast for the constructor that won last years title. This would be slightly better than BOP or success ballast, as you still have real competition within constructors, and in-team team-mate battles remain truthful.
- don't ignore the other classes, promote them. As it is now WRC2, WRC3, Junior WRC, nobody cares about that crap and they barely get a mention in the coverage. The classes need to be uniformized so that the local drivers count towards these side championships instead of being completely ignored, this would hugely increase the number of cars in these classes too. Who gives a crap about WRC2 when it's a total of 3 or 4 cars of journeyman talentless rich guys, because the only ones who have the $ to do the whole calendar, and they're shielded from the much more competitive locals by being scored in a different category with perhaps slightly quicker cars. Sort that out.
- Promote grassroots competition all over the world in national championships, cheap cars, heavily promoted single-car trophies etc. This is how you promote talent, the reason we don't have more Ogiers is that there's not enough people doing rallying, and the few that are good enough don't get the chances to move up the ladder.