Yes, there can be only one SNS swap proposal at the same time and this might become a bottleneck at some point in the future (please note that there can be severals swaps at the same time). As you said, for the time being, this is probably not a big constraint, as every proposals comes with a certain amount of syndication and discussion in the forum and thus in the current stage we all presumably cannot process too many at once anyway.
You do not have to immediately opt in again but could also wait for the next SNS swap proposal (and then re-join). This will still ensure your participation.