So if you haven't been following the news, D.O. from EXO is going to enlist on 1st July 2019. It's probably a huge shock to EXO-Ls, as this was not planned. However, there are more than just "he's enlisting" to this. 

I can almost for sure say he is not going to be an EXO member after he comes out and here's why. 

2019 marks the year for korean members to sign the contract for EXO as they're on the 7+3 contract. So, this is the 7th year, and from earlier this year, we saw D.O.'s news of not sigining. That was the time when all other members signed, and when SM Entertainment didn't announce they all signed, you will know there's a problem. Every time a group re-signs a new 10 (7+3) contract, SM will make a big news about it, consider TVXQ and SJ's 10 year contract. When the news didn't come, I knew something was up. The discussion of re-signing happened last year, as SM needs to know how the members think and make a new contract this year for them to sign. D.O. has been jailed for the whole of 2019, no schedules or whatsoever. This probably is a sign of not reaching a good consensus with SME. 

Here's the logic:

We see last year's comeback as very successful, the album was of great quality. However, it was pushed to so far in the year, this doesn't do EXO any good in year-end award shows. This shows there must be something wrong with the discussion of the contracts. If someone decides not to sign with you again, will you increase or decrease his resources? 

D.O. got less parts, and others got more in the 5th album. We see other members having a bunch of schedules for the rest of EXO 2019 except for D.O. and Sehun. However, Sehun is having a comeback with Chanyeol this summer, so we can reject Sehun as the problem of the contract. Who are we left with then, D.O..

If he didn't re-sign, D.O. is no longer part of SME now, as EXO's debut date was 08/04/2012, thus it's already past 7 years. And April was when he applied to the military, this shows he applied after his contract ended. 

If he did re-sign, why didn't SME make the tour earlier? Why did they have to announce it right after his enlistment news, stating that he's not involved? It's probably because they know D.O. is not going to be there anymore, and wants to use the enlistment as an excuse to hide this for now. (We see stocks of SM falling and rising just because of the news of him earlier this year) If he did re-sign, they could have started the 5th tour right after the album, why wait so long? We see Xiumin having a bunch of resources before he enlisted, a Station song, variety shows. Do we see any D.O. news coming up? Nope. 

We also see SME forbidding D.O. to get his prize last year, for the uprising actor award. Not even a video? Giving his ost solo to Chen, we see SME distributing resources to other people without even consulting the director of the drama.

He has done everything he could for EXO, and he pushed away personal resources just so he could perform with EXO. He has yet to miss 1 EXO schedule because of his own schedules. But how many opportunities has he given up for EXO? D.O. is a calm and determined guy, he knows what's best for him. He knows what he is doing, and nobody blame him if this turns out to be true. He did not WRECK his contract, he simply did not re-sign it. (If this comes out true)

There are a few more "fan explanations" I want to clear up. 

1. He's enlisting to shorten the time of EXO enlisting

- He's a 93liner, he's neither the oldest or the youngest, he's not going to help shorten the time of EXO's enlistment 

2. He's just trying to catch the 3rd series of Along with the Gods

- As of early May, the producer has no plans or have not made plans for the 3rd series. It is highly unlikely that the dates are confirmed. He's going to be in it, but the timing are not confirmed yet. However, this might be a legit reason to why he chose to enlist early as actors peak around the age of 30 and he's going to come out aged 29. 

3. Make EXO vocal line less empty later on. 

- Same reasoning as 1, all the main vocals are enlisting either 2020-2022 or 2019-2021, it's going to be the same 2 years. Him enlisting early has no effect on this situation.

Of course, this is all just my take on this issue. And maybe shed a light to another aspect of the news. Discussions are always welcome below!

Just also another thing, we all know EXO is not really treasured by the company right now, and it's highly likely due to NCT's schedules. I just want fans to calm down, and not blame anyone. There's a time for the baton to be passed on, and the same thing happened to TVXQ, SJ, SHINee when they passed along the baton. There's no reason to be angry at the other groups, as SM is a company afterall. With both SHINee and EXO near enlistment dates, it's all the more important for NCT to quickly build a large fandom so SM will still be earning money. That's why they've been pushing them all over America and the world to boost their fandom.