inputs getting smaller noob here,

am I right in thinking that as bitcoin matures, the average size of transactions, will go up, i.e. higher kb per n BTC, as all the coin gets increasingly spent so that any sizable payment will ultimately end up being made up of increasingly large numbers of smaller inputs, and that this will contribute to the rate at which the blockchain size increases, on top of general total transaction increases over time.. ? With the current large mempool size and delays in getting transactions accepted for mining, except with big fees per kb, will this lead to increasingly large fees to send payments in a timely way or longer delays ??

Thanks
You seem to think that the number of transaction outputs must be higher than the number of transaction inputs. That's wrong.

Just have a look at transaction 19e68405b2ac2f96d5127748ff07bbd629cde93a230582317c9ff50d9644b562 (click me) which has been included in the most recent block. It took 28 inputs from 28 different addresses and produced 2 outputs in 2 address.

The transaction you describe (transactions with a lot of inputs) actually mean that there are fewer UTXO because of them. The transaction I linked to above is very big (8.6 kB) but it destroyed 28 UTXO and created only 2 new ones.

When you're fearing to have to pay higher fees as an individual, you should think about how you actually get many UTXO. If we're talking about a transaction which takes only 2 inputs and has 28 outputs, those 28 outputs will most likely to belong to 28 different people (28 people who retrieved money from an exchange at that time bundled together in 1 transaction or 28 employees payed by a single employer). But in those cases, creating many UTXO is totally justified because they belong to different people. When they spend their money, they unify the money, again, into fewer UTXO.