Adriatic league is a special case because it gives EL/Eurocup spots for its participants , so they do know what they're fighting for.
In the case of Maccabi , Pao and Oly will join Adriatic , it loses it's ex-Yugoslavian national league status & becomes the same strange regional league as VTB.
Maccabi , Pao and Oly won't earn their Euro spots in Adriatic, but in their national leagues . It creates some strange situations : let's say Pao wins, MTA is runner-up & Oly is the 3-rd... Does EL spot belong to the 4-th best team in the competition?
National leagues give spots for Euro competitions is perfectly defined , but with regional leagues starts all the mess:
1) no borders exists, so clubs may shuttle from one regional league to another ( like Nymburk ) in attempt to achieve better results
2) the situation with giving euro-spots for regional leagues is unclear due to (1)
3) clubs play each other in 2-3 different competitions ( e.g. CSKA-UNICS : PBL, VTB, possible EL ) , confusing the fans who need to remember what league do they play & what is the game 'weight'.
4) EL had troubles to separate Adriatic teams & teams from the same countries, imagine separating VTB, Adriatic and national leagues during a draw

There would be no draw at all, all draw will be predefined by the rules.
The system I like is national leagues + long (2-tier ) Euro-season:
Let's say each EL Regular season group ( 6 teams ) - 4 teams go up to Top16, 1 team is going to Eurocup ( second round) & the worst team finishes its Euro season.
The same with Top16 dropouts: 2 top teams go up to Quarters , 1 to Eurocup playoffs & the worst team finishes its Euro-season.
It ensures long Euro season for majority of clubs , eliminating the need in regional leagues. Win-win situation, without the above mentioned mess.