Is the 2.5 way speaker the ideal home speaker?

I think it is helpful to think of speaker design as largely being an evolutionary process based upon consumer demand. There is a reason why large Altec Lansings and Klipsch K-horns gave way to acoustic suspension like the AR3a and KLH to Advent and then to the predominant design of the day-narrow baffled deep floor standers that are ported and either 3 way or 2.5. 
There is a reason too why the outlier designs like planars, wide baffles, open baffles, time arrays, plasmatrons, you name it remain outliers. 
It is largely a matter of being able to deliver the most-looked-for audio attributes for an average consumer's room with an average consumers choice of amplification at a reasonable cost. It is a matter of survival of the fittest. The companies that thrive innovate and evolve and their research and development over time begins to converge on a common solution to these consumer wants. 
In the Preamp/Amp forum someone asked about amplification for the Spendor D7.2 and I tried to help but unwittingly derailed the thread a big when I compared and contrasted the D7.2 with the DeVore O/93's. I own both. I was thinking of this very concept while describing what makes the Spendors so attractive. They do the imaging, soundstage, and midrange things exceedingly well. Most but not all present-day audiophiles want these attributes. Standmounts do these things exceedingly well too at the expense of bass and authority. But again, my main point is that the DeVore O/93's play to a whole different suit of priorities that for better or worse, are sought after by a minority of high-end listeners. I happen to prefer the DeVores but for variety I love the Spendors too. 

Hi. Newbie here. I've been reading this thread with interest and wondered if it might be helpful to briefly summarize the basic rationale behind a 2.5-way design.

It's really a question of performance versus cost. Multiple woofers deliver more bass output than a single woofer. If those woofers are relatively small -- say, 6.5-inch or less -- they should also deliver reasonably good sound in the midrange. However, if they are all operating in unison up to the crossover point with the tweeter, there will be anomalies in the midrange stemming from the physical separation of the woofers. So only one woofer (usually the one closest to the tweeter) is allowed to operate that high; the other (there could be more than one, although I can't think of any examples) is rolled off at a much lower frequency.

A 3-way design should preferable, at least in theory, but it requires an additional type of driver and a more complex crossover network, and both of those increase the cost.

A 3-way design should preferable, at least in theory, but it requires an additional type of driver and a more complex crossover network, and both of those increase the cost.

and often degrades transparency.

I'm not sure I follow, @helomech -

Usually higher tweeter points are achieved with 3-way systems which use a "true" midrange.

It's just my experience that 3-ways often lack the transparency of a good 2-way, I can only guess it's due to the additional crossover components. A good example is the 2-way Maggie .7s vs the 3-way 1.7s. The latter is less resolving.

@helomech

That's interesting, usually three way speakers are considered ideal due to the midrange covering the entire human voice and much of the piano without the crossover involved.

I wonder if your hearing more bass boominess from 3 way designs?