i dont know about the new engine and the current plans with the game and i assume some of the problems getting fixed with the new engine anyway so i just throw in some of the current thinks about the map.
wc3 has problems with a high amount of units(with their collision) so they dont move properly and get stucked for a short time after getting a new order.
on cross you fight 1 side after the other so there are more creeps alive for a longer time which makes it easier to hold cause of the mentioned engine problem and the bad ai which just juggle around or stuck sometimes. this impact is way bigger on cross than on solo build where all sides kill at the same time.
for this reason rounds like 9 and 11 which got a high amount of creeps are fairly easy on 8 player games and way harder on 1-4 player games.
there are more reasons why cross is pretty strong like the double chance of getting good towers but since the last time i played cross active is like 2 years ago i cant recall all of them.
it surely depends on the balacing but in general i would allow crossing on the normal games but disable the possibility on the mastermind mode.
leaking some units to gain more time is a good tactical choice but pushing hard with some units and stall time with the leaks on the king by upgrading regeneration and hp without attack should get more punished or somehow avoided like forcing to upgrade attack after some hp and/or reg or giving the enemy team always 100% of the leaking gold should balance it as well.
an extreme case was common on the old map but can still work on the "fixed" one is to sell all towers on round 4, push hard and upgrade kings hp and reg during this round by stalling time on round 4 and 5 you are able to send a few thousand lumber on round 6 or 7 which is pretty much impossible to hold.
the main problem here is that it doesnt matter if you leak 40 or 100 creeps to the king since he cant be attacked by more then a specific amount maybe 40 for round 5 and 7 but just 16 for round 6 for example which makes it impossible to lose hp on this round which stalls alot of time.
same strategie works after round 7 to send a high amount on round 10 ( my record on the new map was overall 14000 lumber on round 10 and way more on the old map)
on a race(when both teams send and wont survive mostly on round 15 or 17) players build units in the front corner of their side so the incoming creeps change the order of move/attack to attack and stuck for a short time after killing this unit they stuck again before they switch to the move order again this way you can get a few seconds. as a side effect the sent units get blocked and are more likely to stuck in the back with the bigger collision size, take longer to attack and if they leak they reach the king way after the other creeps which deal less damage.
this way the race is not decided which team leaks less units or has more heals.
king can be juggled to stall more time as well (by attacking the opposite creeps of the current one) caused by the turn animation so there should be a fixed attackanimation/time.
pulling units (means attack and kill units from an allied lane) which can be played like cross should be impossible as well on the mastermind mode
well and i guess theres no need to talk about the current antistuck and the abuse of it since those thing wont exist on ltd2
so i hope it the post helps abit and like many others I can hardly wait for the release.
Edit: a system to give each player the same value of sends instead of the same amount would be fine it feels too bad to lose due to 4 demons on the holder lane