There are so many variations of almost every official course, but can we have an additional option to choose one big course containing all 7 smaller parts? I study only Brazilian Portuguese and constant switching between all parts of this particular course is quite inconvenient. I can only imagine how irritating it becomes for people using 4 or 5 official courses.
I think that implementing this option would be rather easy and also very useful to many users like me.
Did you know that some vocabulary repeats between the 1-7 PT BR courses?
There probably is one database per course.
Each course has several levels and words from the course-DB are carefully picked (grouped) and assigned to levels.
What I like about the 1-7 PT BR courses is, that they do not only use single words, but add several phrases/sentences to each level to practice some longer sentences and tenses, subjunctive, etc.
Several courses and levels practice different things…
So how do you want to move all levels and different verbs/phrases to a single course?
Basically you would have to re-work all levels!
Workaround: You can import every course you started to learn with the addon Memrise2Anki to an AnkiSRS single deck.
Either you use the sub-decks or tagging.
Once you merged all seven courses to a single Anki deck, you can learn and review them together without a hard / technical course break.
However having the Memrise streaks for unfinished courses is great and the web UI is so nice.
You also have to be fully aware, that you can extend your Memrise web portal experience, by installing several Tampermonkey user scripts, e.g “Auto correct”, “All typing”, “Audio Provider” by Cooljingle.
Before you are with AnkiSRS to the same level to understand how you shall organize the courses, setup “learning steps”, review settings and fine-tuned all Anki settings you might have finished several offical Memrise courses on their web portal.
And I am telling you that as I am an IT specialist and developer myself.
I started to read the AnkiSRS manual, reading the forum and blogs how to optimize the settings to own needs.
You probably won’t be able to do this within 1-3 days!!!
Take your time to “learn” it and maybe customize AnkiSRS a little bit to the Memrise SR intervals (e.g do you want to have additionally 4h + 12h learning intervals or not, do you start with 1d reviews, shall “easy” be 3/4d, less or more, what external AnkiSRS addons make sense to install; how to play with “filtered decks”, overdueness, etc.).
The only thing which really matters (for me) on the Memrise web portal is, that once you complete a single PT1, 2, 3,… course that your continuous course streak graphic is not visible anymore on the web portal 
I still do not understand why Memrise programmers have done this.
Why to kill a great streak for reviews…
This is one of the reasons that I probably have to port my finished PT 1-5 courses over as 3-5 have not been reviewed so much and 1-2 only 2-3 times, not more.
The reason for me is clearly the streak as the primary reason.
The second reason is, that I am overwhelmed having to review 7+ courses at the same day…especially with typing (“all typing”) instead of AnkiSRS “self-rating answer” (turning OFF multiple-choice).
If DuoLingo staff would kill the course or global (orange flame) streak, the user performance and metrics would probably not be as good.
“Learn PT BR Basics” by Ben is another good course, that uses imperative, past, future, etc: https://www.memrise.com/course/78992/learn-basic-brazilian-portuguese/
If you complete your DuoLingo English-Portuguese tree before or while you do the Memrise courses in parallel, there will come a day where it “clicks” (e.g you see the imperative again in action and you finally understand why the verb ending was “a” rather normal present ending “e” 
I did not the first time, when I only did the course on Memrise as there are zero explanations.
Memrise phrases/sentences often make more sense than DuoLingo sentences
Thank you for your very elaborated answer. I wasn’t aware of some issues you mentioned.
I know Duolingo. Actually I finished their Portuguese course. Now I do it again (“from scratch”) with the new crown system. It’s kinda funny, because we already exchanged a post ot two about the Mondly Portuguese course on the Duo discussion board (you seem to use the same username there, and me too, BTW). Speaking of the Br. Portuguese resources - you should check the new LingoDeer course.
PS.
I would have nothing against “redoing” the whole Memrise course - after all, repetitio est mater studiorum, plus the Memrise official courses have many neat features other similar websites lack.