failure rates where? i've had my samsung ssd for a year now, works like day 1. no moving parts, they have far less failure rate than mechanical drives. According to dell, their ssd laptops have fewer returns than the mechanical hd counterparts. Several other sources also point to SSD's having good lifespan. Mechanical hd's seem they fail more these days than they did in the 90's but thats just me.
Not mature? guy, theyve been around for like 10 years. its only last few they came marketable, they still have some growing room in the technology of course but if we waited for mechanical drives to be mature, no one would by them until probably 2004 or something. i think perpendicular and ssd was the last halfway decent move in hd tech that i'm aware of less you count the hybrids.
technically you had SSDs in the 70s. the first music player ever was around 1970 and used a tiny SSD for a whopping 30 seconds of playtime

. It was a commercial failure because nobody wanted to pay for a player than can store a whopping 0.25 songs
SSDs today are much more reliable then any spindle disk. Early models were much SLOWER then spindle disk and sold purely on being more reliable. only in the past year or so did we finally have greater speed to go with that greater reliability
There are lots of technologies that have been around for a long long time... hydrogen fuel cells were used in airplanes in the 1930s. ePaper has been used in billboards since the 1950s.
There needs to be a certain minimum of performance and cost for something to penetrate the general consumer market though (which requires technological advancements of course)...
there are also alternative flash storage... for example there is a type of SSDs that uses cells filled with a concoction that can solidify as either a crystal or a glass depending on the rate of cooling. By melting it up (run a current through it) and then either letting it solidify (form a glass), or run a light current via it as it solidifies (heating it slightly, causing it to solidify slower, forming a crystal lattice) it can have two separate states. The crystal and glass forms have different electrical resistance which can be measured by running a current via them (too weak to melt it). These drives have neigh infinite writes per cell, and storage duration. (meaning you can do not need TRIM, do not need wear leveling, putting a drive aside without power for 10 years will not cause dataloss, and they should literally last millions of years...)
It is also estimated that as we miniaturize futherther their production cost and reliability will improve a lot compared to current flash storage tech, this tech is available for sale TODAY... however the biggest drives are fairly expensive while only 128MB in space, not nearly the miniaturization level of current flash tech, and are relatively slower.
All of these will greatly improve as their technology is refined, but if you need absolute durability and a small storage those are the drives for you.