The only issue with requiring players to bring a Rebel and Imperial list is that it makes the initial buy-in for a new player quite expensive, just to be able to play in a tournament. Compare to the current model, where, assuming no discounts on pricing and applicable taxes, a new player could bring 3 X-Wings into a match, only having to spend $70 (which in itself is pretty substantial). You can make some decent competitive lists out of just that and have just as good a chance as any at winning a Kessel Run.
Now compare the Imperial side, where we're seeing 5 ships on the table, as a low number that still functions well competetively. The cheapest way would be a Core Set at $40, then another $45 on 3 ship packs, totalling to $85.
Combine the two, where a player would need both lists to play, and you wind up spending less money overall than buying separately, but the inital buy-in is still a pretty large barrier for some people.
2 Core Sets at $80 to have 4 TIE Fighters and 2 X-Wings
1 X-Wing or Y-Wing pack (personal taste) to get to 100pts of Rebels is $15
1 TIE Advanced pack (to use Vader or Maarek to fill in the points) is $15
So total, you're looking at $110 to have your bases covered and be able to get in the door if you're required to be prepared to play both sides and have a reasonable chance at success. Obviously you could technically play with one Core Set and have a really small army list compared to your opponent, but again, the idea is having a a reasonable and fair chance at success at winning.
No, I think this is fine the way it is. As an Imperial player, you need to appreciate that your 8 Academy Pilot TIE Swarm might have a hard time winning out against a literal mirror match of the same list, because of reasons already discussed in previous posts about 2 Attack Dice vs 3 Agility Dice.
As a Rebel player, you need to be wary of someone like Wedge absolutely wrecking your (modified) Agility 1 X-Wing and your (modified) Agility 0 Y-Wing at Range 1. You'll be trying to keep their ships out of Range 1 firing solutions so you don't take massive damage from the 2:1 ratio of primary weapon fire.
The mirror matches really cover extreme case; slow matches with low damage output with Imperials, and fast, high damage matches with Rebels.
If you're not attempting to factor this in, then you're missing the point of what makes tournament games more of a challenge than your casual games. When we play at home, our collection is only big enough to realistically do a Rebel vs Imperial matchup. I don't have a lot of mirror match experience, except for the one I had at Kessel Run.
What I learned from that has me thinking about the Rebel vs Rebel match a lot more now when I build my list for the Toronto Area Kessel Run Round 2 events coming in January. Apparently there were shipping delays so they'll be trickling in throughout the month.
Remember this, fellow gamers, when you want to practice a mirror match at home and you don't have all the "official" models to play it; you more than likely have the actual number of ship TOKENS to make it work. So, if you have 2 Core Sets, you have 2 Luke Skywalker tokens, and 2 Biggs Darklighter tokens, and if you bought 2 X-Wing packs, you now have 2 Wedge tokens, and so on.
Heck, even that notwithstanding, you can ALWAYS go ahead and proxy tokens in at home, just make sure you and your opponent make each other away of what counts as what, and then have at it. All you really need in the game itself is that little cardboard square and the printed fire arc; the model is just fluff and visuals. Use Imperial tokens if you need to for subbing in rebel ships, and vice versa, depending on your personal supply.
The cards and abilities are all easy enough to come across in squad builders, and your own collections, so while it may not look as elegant as having the "official" loadout, you are more than able to practice this stuff at home if you get a little creative.