I'm curious if there are any plants that might add acid to their soil so that they might work well in a permaculture setting, you might be able to plant X, Y or Z near a blueberry bush to eliminate the need for soil upkeep.
About the only thing that will acidify soil over a period of years, and keep it so, are certain trees, mostly conifers, though it varies between species. The variation is accounted for by the presence of calcium in the leaves - the lower the calcium content, the more acid the soil will be. The link below might be of interest on this subject
However, since you're not likely to be planting in a Scots pine forest which has been present for thirty years or more, this isn't much use for your purposes.
Acidic soils are great for potatoes, blueberries, hydrangea...but most vegetables do better in more neutral soils. There are no plants that actually DECREASE the pH of the soil PER SE. Whenever organic matter decomposes some acidity is produced but nothing that would make even a temporary change in the soil to make even blueberries happy. The best way to reduce pH for special acid-loving plants is to add elemental sulfur. This is a slow process and needs to be checked/amended at least yearly. For my blueberries, I add lots and lots of organic matter with periodic applications of sulfur. They are separated from the rest of my garden in their own raised bed. I also plant my potatoes in this bed. I own a great pH sensor...the ones you get at Home Depot or Lowes are pretty iffy. The tests using liquids work better than the 'meter' poke in the ground type. Soil testing truly makes a gardener successful or not...otherwise it is all wishful thinking, grins! And that works pretty well most of the time. Luckily...if someone comes up with a plant that actually makes it's soil more acidic and that this is measurable would be a great thing. Especially when working with pH neutral or more alkaline soils and wanting to grow plants that love acid. If you live in an environment with lots of rain (water produces Hydrogen ions that decrease the pH...especially in conjunction with clay soil) you should have no trouble with acid loving plants. In a dry climate your soil pH will be dictated by minerals, such as limestone and are usually more alkaline. Best bet is to find an easy, inexpensive way to get soil tests. Usually going through your closest University Extension Service is best. Permaculture should entail using what is available versus trying to change anything...planting only those plants that thrive with your soil's attributes. Once we start trying to change things like growing acid loving plants in basically alkaline soils...well, it isn't permaculture anymore. More akin to growing plants in POTS. Totally dependent on us for maintenance.
Well, I suppose there's spagnum moss, but that will take even longer than the pines @Bamboo mentions, and it's not so much the growing as the decay that does most of the acidifying, though a certain amount of "locking up calcium and magnesium" is mentioned in the wikipedia article.
While the classic commercial blueberry barrens are lowland bog-type environments, the good wild blueberries where I grew up were all above treeline (good sun) on granite mountains (no nasty, nasty limestone,) basically growing in cracks and hollows in the rock that they had composted by themselves for a long time with blueberry leaves and a bit of bear (& etc.) manure.
All plants roots acidify the soil by stimulating microbial life in the soil and releasing organic acids. Any organic life can result in a buildup of organic debris over time which breaks down into humic compounds (organic acids) over time in a process known as soil acidification through biological weathering - forest soil is the most acidic because this occurs at the greatest rate there due to the high density of life. This is on a longer time scale than you need.
You could possibly achieve your goals using a fungal innoculation along with a one time chemical soil amendment.
"Adjusting Soil pH: When planting oaks or other acid-loving plants into neutral or alkaline soils, it is often a good practice to incorporate a soil-acidifying additive (like sulfur) along with your mycorrhizal inoculum. While this will only reduce the pH temporarily (a few weeks), it will allow the mycorrhizal fungi to colonize the roots while the pH is low. Once the fungi set up residence within the root tissue, they can take refuge from the higher soil pH and work to increase acidity inside the fungal sheath. Subsequently, as soil pH in the planting hole gradually rises, the mycorrhizal fungi are already well-established and capable of controlling the pH of the roots’ micro-environment."