The vast majority of most boats on lakes are gas. The vast majority of most boats below 35' are gas. So clearly there is a place for it. Now, determining where that is and isn't may be more difficult.
The first thing I did was look at the largest seller of boats in the 30-50' range, Sea Ray. They use gas engines with stern drives up through their Sundancer 370 and start using diesel with straight drives and/or zeus pods on their Sundancer 410 and larger.
I do think the drive you're coupling to has a role to play. Stern drives predominate under 40' and straight drives and pods above.
For the average user of a boat in the under 40' range, gas will be less expensive, not just to purchase but over the life of their usage. On a Sundancer 370, a Yanmar Diesel adds $34,000 to the price of the boat or about 8% of the base price. However, on stern drives they're now offering options such as Axius and Sea Core so the diesel is only $7,500 over the most expensive outboard.
The diesel in the above case, however, will underperform the gas engine, so it's not the appropriate choice for the majority of purchasers of that boat. It would perhaps be a great choice for a trawler like purchaser though who intended to use the boat mostly at lower speeds.
I have a rather simple example of the effect of diesel on a small boat's performance by using an extreme case. Williams makes a 445 tender, so just over 14'. With a 100 hp gas engine it has a WOT of 42 knots. With a 100 hp diesel it has a WOT of 32 knots. Why? The single diesel engine adds 900 pounds of weight, taking the weight of the boat from 950 lbs to 1850 lbs. So the weight difference is an issue. It becomes less so as the size of the boat increases and as the owner is less concerned with getting top speeds.
At the time many of these older boats were built there was another issue. Diesel fuel cost much more per gallon than gas. Now, on the waterway, it's reversed due to most non-marine gas containing ethanol. Non ethanol gas right now runs 60 to 90 cents per gallon more than diesel. So the economics have turned dramatically. Now you're talking savings on fuel usage and price with diesel.
The average boat on a lake is used less than 100 hours a year. At that usage there is no reason not to go with gas engines. Fuel consumption doesn't matter. Weight and purchase price do. Also space within the boat. Inboard outboards take far less space inside.
Now for coastal usage there's one more issue. Historically, stern drives didn't survive salt water well. This has been greatly improved with things like Seacore, but a straight shaft can still handle the conditions better.
If I was a light to moderate user and found the boat I liked with gas engines, they passed the survey with flying colors, then I wouldn't hesitate to buy it. I ran nothing but gas engines from the time I was 13 until I was 43. I only knew there were diesel boats peripherally. If the boat is what I want and does what I want then gas it up.