The QBO has been a focal point of investigation in recent years. This upcoming season, La Nina + EQBO, is pretty interesting wrt the MJO. Here's a couple relevant points from the following article.
Combined effect of the QBO and ENSO on the MJO:
https://www.tandfonline.com/doi/full/10.1080/16742834.2019.1588064
For each La Niña/QBOE year (Figure 3(c)), there are 1.7 MJO events, which is much larger than that in an El Niño year and La Niña/QBOW year. The last phase has only 0.6 MJO events (Figure 3(d)). During a La Niña/QBOE year, the MJO can propagate to the western Pacific without being suppressed over the Maritime Continent. During a La Niña/QBOW year, the existing MJO is observed to be enhanced over the Indian Ocean, while it is barely able to pass the Maritime Continent (Figure 3(d)).